History VideoGame / BlackMesa

** [[spoiler:The Nihilanth's tower]] outright '''explodes''' after its owner is defeated. {{Justified}}, though, [[spoiler:as this is the result of the psychic backlash from the Nihilanth exploding]].

** The balaclava shotgunner soldier is merged with the standard gas mask soldier, who is able to use either the MP5 or SPAS-12 (alongside the newly introduced corpsmen variant). HECU Commanders have adopted the Grenadier's unique ability to use the MP5's underslung grenade launcher, with Grenadiers now wielding single-shot, disposable Rocket Launchers.

** The final surface portion of the original (set at the end of "Forget About Freeman!") consisted of the player fighting a pair of HECU troopers and a tank. In the mod version, the soldiers are more numerous, a trio of Ospreys is fleeing the base, and several alien aircraft are engaging Apache gunships and jet fighters in battle. In the release version, [[SerialEscalation the HECU has several vehicles but, save for the tank, all of them are destroyed by an alien aircraft]].

** The final surface portion of the original (set at the end of "Forget About Freeman!") consisted of the player fighting a pair of HECU troopers and a tank. In the mod version, the soldiers are more numerous, a trio of Ospreys is fleeing the base, and several alien aircraft are engaging Apache gunships and jet fighters in battle. In the release version, [[SerialEscalation the HECU has several vehicles but all, but the tank, are destroyed by an alien aircraft]].

The time put into developing the game certainly [[DoingItForTheArt shows]]: beyond the numerous graphical improvements and greatly increased environmental detail, each level has been updated and expanded, with the entirety of Xen having been redesigned from the ground up; characters behave in a more realistic and, in the case of enemies, challenging manner thanks to improved animations and AI enhancements.

** Dr Smithers, the scientist found next to the rocket test silo's generator, is notably paranoid and shamelessly admits to leaving his colleagues for dead, declaring the situation is "survival of the fittest".

*** With this new input layout comes the ability to use the module ''omnidirectionally'', which not only offers greater control over player mobility while navigating Xen's floating islands but also allows the module to fulfil more combat-centric applications, allowing the player to quickly and more effectively sidestep and backpedal out of harm's way. Mastery of this movement is ''mandatory'' if you're going to stand a chance against Xen's bosses.

** "Tittles" instead of "Skittles", "Nekid Fries" instead of "French Fries" and "Coca-Bola" instead of "Coca-Cola". On the more creative end of the spectrum is "Alpine Hue" (Mountain Dew) and "Rambler's" (Walker's, or Lay's in the US).

** The Black Mesa [=SUVs=] are modelled after Jeep Cherokee XJ's with "JOOP" badges.

*** After you blow up the casserole in the break room, a scientist mentions that they'll never hear the end of this, while a security guard encourages Gordon to leave quickly, mentioning "That was You-Know-Who's lunch". In ''Half-Life 2: Episode 2'', you meet the supposed "You-Know-Who"; Dr Magnusson, who is still mad at Gordon for this incident, over 20 years later and after the collapse of human civilization.
** The game has female scientists alongside male ones. While the male ones retain their vocal and sometimes visual resemblance to Dr Kleiner, the females all but shout "Dr Mossman" in theirs.

** In an EasterEgg location in "Surface Tension", you can find Dr Breen's poorly spelled, [[TerribleArtist drawn]] plans for world domination, which involves befriending aliens and getting them to build him a huge tower, seemingly predicting the Combine and their Citadel in ''Half-Life 2''. You also learn that he really, really, ''really'' doesn't like Dr Vance.

*** Plus an extra one for ''Episode 1'' in the hidden research centre you find in the area: [[spoiler:A voicemail of Barney talking about the scientist ends with Kleiner locking himself out again, making the guard rush to beat Gordon who was already halfway through the vents.]]

** The balaclava shotgunner soldier is merged with the standard gas mask soldier, who is able to use either the MP5 or SPAS-12 (alongside the newly introduced corpsmen variant). HECU Commanders have adopted the Grenadier's unique behaviour of being able to use the MP5's underslung grenade launcher, with Grenadiers now wielding single-shot, disposable Rocket Launchers.

** A security guard also tells Gordon to say "Hi" to Dr Cross, the HEV suit training instructor and one of the main characters in ''VideoGame/HalfLifeDecay''.
** On one of the bulletin boards is a note from Otis that Security Desk B3 needs more doughnuts, Otis being the fat security guard NPC introduced in ''Opposing Force'' & ''Blue Shift''. You even find one instance of him holding a doughnut instead of practising at the firing range in ''Blue Shift''.

*** The HECU snipers are the Combine snipers in everything but name; Like in ''Half-Life 2'', they're an invisible entity that can only be killed via explosives, rather than ''Half-Life'''se concealed brush of a human shooting target that can be killed with traditional means. Their firing positions are also revealed by laser sights, coloured red instead of the Combine Sniper's blue.

** "Interloper" is just ''massive'', rivalling the updated "Surface Tension" in length.

*** It's only at the end of the "Xen" chapter do you reach that all too familiar island, and even then, it has a significant number of changes that make it a far cry from its ''Half-Life'' appearance. For starters, you don't arrive from a set of moving platforms floating above the island. Rather, you enter it from the side by crossing twisted bridges of knotted roots. While the exterior is still guarded by hanging alien turrets and packs of Houndeyes, the interior has received a drastic overhaul; the waterlogged room with the barest pretence of a puzzle is now replaced by a snaking network of smooth tunnels, linking to rooms containing three beam emitters and a control room, all made from a never-before-seen technology; too alien be human, too organic to be Combine. This network becomes the centrepiece of a series of puzzles, as you navigate through the island's interior and exterior in order to repair the damaged teleporter generator, socket-switching and hunting around for Xen crystals to power its components. To sum it all up, it's basically a revamp of the Citadel core puzzle from ''[[VideoGame/HalfLife2 Half-Life 2: Episode One]]''.

** A piece of paper taped to a wall in Xen shows the expedition's kill tallies of various alien creatures. Houndeyes are nicknamed "[[Franchise/SonicTheHedgehog Sonic the Bull Dog]]" and [[spoiler:fire Houndeyes]] are called "[[WesternAnimation/TheSimpsons Mr Burns]]".

** The HECU's vehicular lineup is more consistent with what the U.S. Marines would use (M2 Bradleys and F-16s from the original are replaced with LAV-25s and AV-8B Harrier [=IIs=], respectively), they correctly refer to their medics as "corpsmen" and their first aid kits as [=IFAKs=][[note]]Individual First Aid Kits[[/note]] in the retail release, and they use protective gear modelled after real-world equipment including the [[https://web.archive.org/web/20130618122028/http://i146.photobucket.com/albums/r261/ArvinPabico/armorvest-Crye-armor-7.jpg Crye Precision Armor Chassis]] and the [[https://web.archive.org/web/20160327140300/http://wwww.specwargear.com/retro/images/helmet-CCT%20IBH-1.jpg Integrated Ballistic Helmet]].

* AdaptationalHeroism: While players familiar with ''Half-Life 2'' onwards already know that the Vortigaunts are nowhere near as malevolent as they seem, ''Black Mesa'' takes pains to show that they really were in a bad way before Gordon killed the Nihilanth, emphasizing their sympathetic traits. In the original game, the Vortigaunt slaves in Xen would attack Gordon Freeman on sight... except in the first area of the factory, where they would only retaliate if Gordon attacked them first. In ''Black Mesa'', the Vortigaunt slaves in Xen are clearly shown to be oppressed and will never attack Gordon unless explicitly controlled by an Alien Controller, [[spoiler:and they even help him progress by shutting down forcefields and alarms]]. In general, the "Slave" part of their [=HL1=]-era name[[note]]monster_alien_slave[[/note]] is played tear-jerkingly straight. The very first time you find any Vorts in Xen, they're being brutalized for no reason by a pair of Alien Grunts, several Vorts crying and begging for mercy. Throughout the remainder of the game, you can find plenty of evidence of their sorrowful state, and [[spoiler:TheReveal that Alien Grunts are merely Vortigaunts who have been twisted into hulkish monstrosities]] only drives the point home. The Vortigaunts are being forced to [[spoiler:operate the machinery that is turning their kin into horrible monsters, and given their shared consciousness, odds are they know it.]]

** Dr. Smithers, the scientist found next to the rocket test silo's generator, is notably paranoid and shamelessly admits to leaving his colleagues for dead, declaring the situation is "survival of the fittest".

** While the Gonarch is ''significantly'' more aggressive toward Gordon here than it was in the original game, it's actions are given more nuance in ''Black Mesa'', as the BossBattle with it lasts ''the entire chapter'', during which Gordon not only kills many of its offspring, but also tears apart its nest trying to find a way to the Nihilanth's tower. [[spoiler:It even tries to retreat during its final confrontation with Gordon, only for its strength to fail, forcing it to fight Gordon to the death]].

** The HECU is given a couple of moments to make the player empathize with them, such as a wounded marine being given triage instructions by a medic over radio, only to expire mid-conversation. Another scene has two marines wonder why they are even fighting here, with one admitting it feels wrong to gun down scientists who won't fight back. Finally, the last major surface battle has the HECU desperately trying to retreat from the facility, with those that fight Gordon becoming trapped after an alien craft fries all of their vehicles except a tank (which can't clear out the wrecks, leaving it trapped in the area as well).

** The LaserHallway building in "Surface Tension" is greatly increased in size and there's even MORE mines in it than before. As part of Update 1.0, "Surface Tension" received a gameplay overhaul, which included even '''''[[NoKillLikeOverkill MORE]]''''' trip mines in the warehouse.

** All of the chapters taking place in Xen, from "Xen" to "Nihilanth" have been expanded significantly. Where ''Half-Life''[='=]s Xen chapters could be played within an hour, ''Black Mesa'''s take on the chapters now take about four-six hours, assuming you don't explore. New areas include [[AbandonedLaboratory overrun expedition labs]] and [[BubblegloopSwamp lush swamps]]. New enemy variants also appear, including [[spoiler:two new species of Houndeye and ZEV (HEV Zombies)]], and a couple of sections are dedicated to puzzles which are completely seamless with the new environment. Plus, in addition to the healing pools from ''Half-Life'', energized blue crystals appear which charge up the HEV suit just by standing near them.

** The HECU Artillery gun from the dam segment of "Surface Tension" is gone, having instead been replaced by an M2 Browning machine gun emplacement, with the primary opposition instead being several squads of soldiers and the Apache. The Tentacles encountered in the next map are also absent, with a mine-turned toxic waste dump in its place.

* AIIsACrapshoot: Like the original, the Black Mesa ceiling turrets do not discriminate between friend or foe and will gun down whether they are Black Mesa employees or the Xen aliens. Justified as it's implied that the HECU took over the facility's defense systems (like they did with the announcement system) and reprogrammed them to attack any employee inside as part of their cover-up operation. This doesn't count for the turrets outside the Supply Depot in "Lambda Core", where they recognize Freeman as a friendly, being one of the facilities that wasn't taken over by the HECU.

* {{Antepiece}}: In addition to those present in the original game, there are a few more added in here.

** The first Xen teleporter you find is connected to a fleshy mass with a crystal inside it. When you go into the forward base, you'll find a door that needs power, with the same mass from earlier emitting electricity that surges toward the plug, telling you that the masses can be used as power sources. Finally, a second mass is encounter further into the base, but this one does not have a crystal in it. Nearby, however, is a specimen marker with a very specific looking crystal in it, which you can insert into the mass. All of this preps you for a much more complex challenge that makes up the final portion of Xen.
** Your first encounter with Vortigaunts in Xen has them cowering in fear from Alien Grunts. No matter what you do, they will not attack you. A while later, while going through the Vortigaunt slums, you accidentally raise the alarm, summoning several Alien Controllers. Said controllers promptly begin firing green beams at the Vortigaunts, who then begin attack the room you are in. Once you kill all of the controllers, you'll jump to the ground, where the ground-level Vortigaunts are cowering in fear. This tells you three things: that Vortigaunts in Xen are no longer hostile, that Alien Controllers can ''make'' them hostile again, and killing the Controllers will revert the Vortigaunts back to normal.

** The Long Jump module received a massive overhaul in preparation for the Xen chapters, which ensure that any jumping sections within the border world are far less aggravating than they were in ''Half-Life'':

*** With this new input layout comes the ability to use the module ''omnidirectionally'', which not only offers greater control over player mobility while navigating Xen's floating islands but also allows the module to fulfill more combat-centric applications, allowing the player to quickly and more effectively sidestep and backpedal out of harm's way. Mastery of this movement is ''mandatory'' if you're going to stand a chance against Xen's bosses.
*** By tapping any directional key while in the middle of a long-jump, the player can activate jets to influence their mid-air trajectory in that direction once per-jump. This grants the player the ability to either correct an off-course jump or prevent themselves from overshooting their intended target.

* ArmiesAreEvil: Downplayed from the original game. While the Hazardous Environment Combat Unit retain all of their villainous intentions from the source material, they're more humanized in this game, and various radio transmissions heard throughout "Surface Tension" only serve to further elicit sympathy towards these marines as they're increasingly overwhelmed by the invading Xen forces.

** The Marines now use more appropriate vehicles (the Bradley was replaced with a LAV, the F-16s were replaced with AV-8B Harrier [=IIs=], Humvees are also present with the trucks) and wear more realistic looking uniforms (the "powered combat vest" was replaced with modern plated body armour and they no longer wear balaclavas). The various mortar pieces throughout "Surface Tension" were also replaced by TOW missiles, and the weird double turrets in "On A Rail" were replaced with normal M2 Browning machine guns.

** Zombies now come in Security Guard, HECU and HEV variant, the latter two dubbed by Crowbar Collective as the ZECU and ZEV respectively. In ''Half-Life'', Security Guard Zombies only appeared in the Gearbox Expansions ''Opposing Force'' and ''Blue Shift'', while ZECU were exclusive to ''Opposing Force''. The [=ZEVs=] an entirely original enemy added to Xen. In addition, headcrabs can now detach from defeated Zombies if the elimination method didn't involve a headshot, a feature in ''Half-Life 2'' that was supposed to be implemented in the original ''Half-Life'', but was ultimately cut due to being too complex.

** The HECU Marines. They flank, use teamwork, throw grenades to flush you out, and cover each other just they did in ''Half-Life''. They can now also shoot while moving and provide suppressing fire on your last known location, and will retreat whenever they're wounded or at a tactical disadvantage.
** All enemies are significantly smarter, not just the marines. Even Vortigaunts will use basic squad tactics, like covering each other and flanking.
** In "Power Up", you could escape the Gargantua in the first game through a door while he was distracted with killing HECU marines, and it would forget about you until you wandered in again. Not this time. The monster goes right to the door you went through after its killing spree and ''actually reaches in with his flamethrowers'' if you're near it. Suffice to say, a lot of players [[StealthPun got burned]] by that one unexpectedly.

** The double-barreled shotgun blast can do a LOT of damage and can straight up one-shot most standard HECU grunts and, if [[WebVideo/SamONellaAcademy RNG-esus]] is on your side, Vortigaunts. Problem is, the fire rate is worse than the regular shotgun blast, and you have to get really close and personal in order for it to even have a chance at doing any damage. Not to mention it takes two whole shots of your precious shotgun ammo.

** Gordon Freeman is a theoretical physicist who found himself in midst of a literally out-of-this-world catastrophe he unwittingly contributed to, but nevertheless managed to run, think, shoot and live through the Black Mesa incident even as the facility descended into an alien-infested war-torn nightmare with nothing more than his above-average fit body, his wits, his protective HEV suit and a diverse collection of mundane and exotic weapons he picked up along the way.

** The [=MP5=] is a mixed case. Its 40mm grenades don't do as much damage and have a smaller blast radius, it doesn't have it's fifty round capacity like it did in ''Half-Life'' -- now replaced by an ordinary 30-round mag -- and its reserve ammo was cut down significantly (from 250 rounds to 150, and from 10 grenades to 3), while also suffering from considerable recoil when fired in long bursts. Despite these drawbacks, the retooled [=MP5=] is compensated with a faster rate of fire and drastically improved accuracy (especially if fired in 3- or 4-round bursts), the latter thanks to its bullet spread being based on bloom as opposed to a fixed cone. Additionally, its damage-per-bullet is now equal to the Glock as opposed to being less (appropriate, given that both weapons share the same ammo pool) and its grenades now travel much faster through the air.

** "Tittles" instead of "Skittles", "Nekid Fries" instead of "French Fries" and "Coca-Bola" instead of "Coca-Cola". On the more creative end of the spectrum are "Alpine Hue" (Mountain Dew) and "Rambler's" (Walker's, or Lay's in the US).

** The added detail available from the new Source engine allows for unprecedented levels of gore in ''Black Mesa''. Along with the usual blood splatters from kills, almost every enemy can be gibbed by explosions or especially powerful weapons, while blood (both human and alien) and Bullsquid acid will regularly splash on Gordon's arms and weapon in disturbing detail should he be injured, attack an enemy up close, or get caught in an enemy's gibbing.[[note]]This is disabled by default in the retail release due to an unresolved lag spike when the effect first occurs, but can be re-enabled with console command '''cl_mdldetailfx_enable 1'''.[[/note]] Dismembered body parts also litter Black Mesa.

** The game has female scientists alongside the male ones. While the male ones retain their vocal and sometimes visual resemblance to Dr. Kleiner, the females all but shout "Dr. Mossman" in theirs.

** In an EasterEgg location in "Surface Tension", you can find Dr. Breen's poorly spelled, [[TerribleArtist drawn]] plans for world domination, which involves befriending aliens and getting them to build him a huge tower, seemingly predicting the Combine and their Citadel in ''Half-Life 2''. You also learn that he really, really, ''really'' doesn't like Dr. Vance.

** The last portion of the chapter "Xen" features an expanded version of the teleportation activation sequence in ''Half-Life'', set in an alien facility which bears a remarkable similarity to (and contains a very similar puzzle from) the Citadel Reactor Core in ''Half-Life 2: Episode One''.

** The entirety of Xen is, in many ways, calling forward (and inspired by) the design philosophies of ''Half-Life 2''. The most evident is the "see the destination" guidance method Valve used, making the Combine Citadel visible throughout the game as a reminder of the player's purpose. In Xen, the equivalent of this is the ominous, towering structure housing Nihilanth and the Alien Grunt factory. It comes progressively closer into view as the player travels across Xen, and eventually, you are required to scale it from within. In addition to making Xen seem ''smaller'', this also gives the alien dimension some much needed visual coherence, since it's no longer a disconnected set of isolated maps but more like an actual ''place'' you can understand.

*** Plus an extra one for ''Episode 1'' in the hidden research center you find in the area: [[spoiler:A voicemail of Barney talking about the scientist ends with Kleiner locking himself out again, making the guard rush to beat Gordon who was already halfway through the vents.]]

* TheCavalryArrivesLate: During the last third of "Surface Tension", Gordon overhears an Osprey with the callsign Goose-4 calling for aid as it prepares to take off, with the LAV Bloodhound-3 acknowledging and moving to support them. A couple of seconds later, you witness Goose-4 be destroyed by Vortigaunts just before Bloodhound-3 bursts through a nearby gate (and then gets destroyed by newly arrived Xen forces).

** Required in the first part of "Unforeseen Consequences" - you don't get a Crowbar right off the bat. Instead, you need to chuck flares at the zombies to set them on fire and/or get them into your accompanying security guard's line of sight.

** Another achievement is awarded if your killing blow on the Gonarch is made with the crowbar.

** The final segment of "Gonarch's Lair", in a similar manner to the original game, is demolished ''during the fight''. Towards the end, the ceiling collapses and sends you into the bottom of the arena. The Gonarch tries to flee as this happens, only for its strength to finally fail and send it hurtling to the bottom, where the now horribly wounded creature continues to try and kill Gordon until it is finally put down.

* CombatMedic: [[ShownTheirWork Correctly called "corpsmen" in this game]], these are a new class of HECU Marine carried over from ''VideoGame/HalfLifeOpposingForce''. Like their predecessors, they will heal fellow HECU Marines should they get wounded in the field. Unlike their predecessors, the corpsmen are armed with the same weapons as regular HECU marines ([=MP5s=] and SPAS-12s as opposed to Glock 17s), and are just as competent as them.

** Instead of Freeman facing off and destroying three different AH-64 Apaches in "Surface Tension", here Freeman only fights one helicopter twice: first at the Sector G Hydroelectric Dam, where it gets heavily damaged and retreats, is then seen flying around during the drainage pipe segment and is finally finished off with the RPG during the cliff standoff.
** The balaclava shotgunner soldier is merged with the standard gas mask soldier, who are able to use either the submachine gun and shotgun (alongside their newly introduced corpsmen). The grenadier soldier is merged with the commanders, who are the only ones able to use the submachine gun's grenade launcher.

** On one of the bulletin boards is a note from Otis that Security Desk B3 needs more donuts, Otis being the fat security guard NPC introduced in ''Opposing Force'' & ''Blue Shift''. You even find one instance of him holding a donut instead of practising at the firing range in ''Blue Shift''.

* CouldntFindAPen: In addition to the scientist in the Lambda Complex who wrote the solution to a nearby puzzle this way, there's also the military's messages to Gordon during "On A Rail", which were written with more mundane implements in the original game. Halfway through the chapter, "DIE FREEMAN" can be seen written with the blood of a dead security guard, and the highly popular [[GameMod "Uncut" mod]] for the chapter features the rest of the original messages, in all their poorly spelled glory, also inscribed in blood.

* CurbstompCushion: Downplayed. Unlike the original where the HECU tend to win individual skirmishes against Xen aliens, it's the other way around in the remake due to their lack of [=PCV=]'s (which is reflected by their lower base Hit Points) and as well as the AdaptationalBadass treatment of Xen's military. This is best seen in "Surface Tension" where its not uncommon for HECU to lose individual skirmishes to the Xen invasion force.

* DeathWorld: '''''Xen'''''. Dear God, Xen. With the reworks massively expanding the Xen levels, the players can now truly apprieciate just how deadly the border world is as it is beautiful.
** Think Barnacles are bad? In Xen it turns out they have an aquatic counterpart nicknamed 'Beneathacles'. You can get dragged by them underwater while taking a swim, though they are actually easier to spot.
** Houndeyes are dangerous in packs with their sonic area-of-effect attacks. In Xen, they have an orange, glowing explosive counterpart which charges at you en-masse and blow you up unless you act quickly.

** During the first battle with Gonarch in "Gonarch's Lair", there's a floating island in the arena that contains a healing pool and a supply cache which the Gonarch cannot reach. However, should the player attempt to camp there, [[spoiler:the Gonarch will first start shooting them and then ''throw chunks of the environment at them''.]]
* DiesDifferentInAdaptation: In the original "Surface Tension Uncut" add-on created for the mod, an Osprey is destroyed by an Alien Aircraft as it prepares to take off and evacuate several wounded HECU. When the add-on was officially implemented in the retail release, this was changed; the Osprey is instead destroyed by Vortigaunts blowing up a tanker parked near it (implied to be used for refueling).
* DifficultyLevels: The usual '' Half-Life'' convention of "Easy", "Normal", and "Hard" difficulties is thrown out in favor of instead calling the difficulties "Normal", "Black Mesa", and "Hard". On Hard, the HECU are far more aggressive, while the Assassins, like their original counterparts, will use invisibility cloaks. Meanwhile, Normal makes both the HECU and Assassins less aggressive, and removes the Vortigaunts' ability to dodge incoming fire.

** Isaac Kleiner, Eli Vance, and Barney Calhoun are retroactively implemented in place of generic [=NPCs=] from the original ''Half-Life''. Kleiner and Eli are featured as two of the scientists overseeing the experiment in the Anomalous Materials lab, with the latter taking the role of the scientist urging Gordon to find help topside as implied in ''Half-Life 2'', while the guard in front of a locked door during "Inbound" closely resembles Barney, right down to his lack of gear at that time as demonstrated in ''VideoGame/HalfLifeBlueShift''.

* EasilyThwartedAlienInvasion: Subverted. Like in the original ''Half-Life'', while the HECU manage to contain the extra-universal alien incursions at first, as time goes on the AlienInvasion becomes more organised and coordinated, leading to the HECU gradually losing ground and becoming increasingly desperate as they are overwhelmed by both sheer numbers and powerful alien soldiers and machinery/monsters like the Grunts and the Xen Manta Rays. The situation gets bad enough that by "Surface Tension" and "Forget About Freeman" the US government issues an evacuation warning for the ''entire state of New Mexico'' as the HECU retreats in utter rout, showing how badly shit has hit the fan.

** Through use of the console, the VOX system can be used to [[https://youtu.be/q-i0M-PdUS4 say nearly anything.]]

** The plant tentacles are first seen in a swamp in Xen, impaling an unaware Bullsquid. Explosive fauna located next to some help dictate to the player that they can be destroyed.

** A relatively easy to miss example is the Beneathacle, an aquatic Barnacle, eating up an HEV corpse. It can be easy to miss due to the underwater view.
** The first level in "Interloper" shows Vortigaunt slaves being abused by their Grunt equivalents, which help clue in the player that the slaves are docile in their homeworld. Later on, the Controllers appear and start brainwashing those slaves, turning them berserk.

* EveryPizzaIsPepperoni: Every pizza found throughout the game is pepperoni-flavored. The menus posted in the facility's various cafeterias also list cheese and tomato pizza, although it's nowhere to be seen.

*** The HECU snipers are the Combine snipers in everything but name. Like in ''Half-Life 2'' and unlike the original game, you explicitly need to use explosives to kill them for good, rather than just deal damage to a cardboard cutout. You can spot them by their laser sights.
*** The Bullsquid borrows the acid attack from the Antlion Worker. It takes more effort to avoid this attack than their original counterparts.

** In ''Half-Life 2'', Barney's first line concerns the beer he owes Gordon, a reference to the pre-disaster security guard dialogue about sharing a beer with Gordon after work. But these lines aren't said by Barney, who is canonically the guard originally seen at the start of the tram ride, and could not have made it to the Sector C labs before Gordon. This is rectified by instead having the guard at the Sector C tram station reference the fact that Barney's bar tab is past due and that he relies on others to buy drinks for him. Of note is that the original dialogue about sharing a beer is still in this game, albeit slightly changed:

** Similarly, the scientist that gets fussed about the exploded microwave casserole and would eventually become Magnusson uses Kleiner's model in the original game. In ''Black Mesa'', neither are present in the staff lounge, and the [=NPCs=] instead mention that currently not-present "you-know-who" (Magnusson) will get extremely upset with Gordon's antics if he chooses to blow up the casserole.

* FromBadToWorse: "Surface Tension" and "Forget About Freeman!" make it clear that things are going to both within and outside of Black Mesa.
** As Gordon progresses across the surface, the HECU gradually lose ground against the Xenian invaders, with their appearances diminishng throughout "Surface Tension" while Xen forces take their place. Radio transmissions heard throughout the chapter further expand on this, with many marines ''beggging'' for reinforcements or evacuation.
** The Emergency Broadcasts become gradually worse and worse. The first warns the public a disaster has occurred at Black Mesa and recommends evacuation of a 75-mile radius around the facility. The second increases that evacuation area and orders everyone to leave, while hinting that an infection is spreading from Black Mesa. The final one basically spells out an alien invasion is underway, that the U.S. military has gotten its ass kicked and the President is ordering Black Mesa nuked. It orders an evacuation of ''all of New Mexico''.

** Partially, as the devs have stated that some players randomly crashing at various points in the game, whether always at a specific position or just from playing for a while, is not their fault, but the Source engine's from being a bit overstressed by the game.

* GeniusesHaveMultiplePhDs: The game features a minor scientist who complains that the button-pressing he's confined to performing is beneath him because he has two [=PhDs=] and an Oersted Medal, which may be interpreted as a dig at how Gordon Freeman, both here and in the original ''VideoGame/HalfLife1'', is made to do grunt work in the Anti-Mass Spectrometer despite being a doctorate holder. The Hazard Course mod takes this further with some dialogue that implies that a large majority of the scientists employed at Black Mesa hold multiple [=PhDs=], and Gordon with his single [=PhD=] in theoretical physics is actually an outlier.

* GodzillaThreshold: The third and final Emergency Broadcast message found in "Surface Tension" offers a glimpse to the world outside of Black Mesa, and things are looking real bad. Since the HECU are unable to contain the alien invasion, the President has declared a state of emergency, ordered an immediate withdrawal of all ground forces, and begin immediate airstrikes over Black Mesa, and has ordered the ''entire state of New Mexico'' to be completely evacuated of all civilians ASAP. Things are getting so bad that the Emergency Broadcast also requests any civilian with any amount of military or firearms training to immediately report to a military officer, suggesting that the army is making an [[LoweredRecruitingStandards emergency recruitment effort]] to hold back the invasion.

* HyperactiveMetabolism: Drinks from the vending machine can heal you, with each can equating to 1 HP. You can either have the machine dispense one drink at a time by pressing its buttons, or, if you're impatient, just smack it with a crowbar to have it spew out all the cans at once.

* LastStand: The final surface battle in "Forget About Freeman!" has been converted into one for the HECU. As Ospreys flee overhead amidst jets and helicopters dogfighting alien craft, a HECU convoy on the ground tries to flee, only for the majority of their vehicles to be zapped by an alien craft as Gordon emerges from underground. The survivors engage him in battle, only to be cutdown.

* LikeCannotCutLike: The Hivehand's primary fire has no effect on exploding Xen plants or other Xen obstacles, because it only homes in on enemies, while the aforementioned obstacles are hazardous objects. The secondary fire will still work, though, because this turns the hornets into unguided missiles.

* MadScientist: Implied with Black Mesa, since the comments and activities depicted throughout the facility suggests that Black Mesa had been up to all manners of research and inventions - many of which are implied to be dangerous, unethical, illegal, or any combination of three. At best, one scientist fears it would lead to a media circus that would ruin their careers and the company, and at worst it would kill everyone in the facility if not endanger all life on Earth. As events shown, those fears were very real.

** "Interloper" is just ''massive'', rivaling the updated "Surface Tension" in length.

** The security guard stationed at the aforementioned security checkpoint berates Gordon for cutting his ponytail, which was present on his model in the original ''Half-Life''.
** The computer in the Sector C lobby that Gordon can fiddle with has an IM conversation between two of the scientists from ''Half-Life'', conversing via [[MadLibsDialogue their old generic dialogue lines]].

** The same scientist also mentions that he designed the underwater breathing apparatus for the suit, but it didn't end up being used. This is a reference to an oxygen tank for the suit which was cut of the original ''Half-Life''.

** The Black Ops female assassins appear to be wearing modified, all-black [[VideoGame/{{Portal2}} Long Fall Boots]], which explains how they can jump around without breaking their legs. It's also rather funny when you realize that not only are the military trying to eliminate the Black Mesa Research Facility, they're doing so with gear from the company's primary competitor. Also notable is that the boot's predecessors, the [[VideoGame/{{Portal}} Advanced Knee Replacements]], were a recycled prop from WhatCouldHaveBeen the Black Ops' successor in ''Half-Life 2'', the female Combine Assassin. What's more, Assassins now dual wield pistols, another trait they share with their cut descendants. In the original game, they had only one.

** In general, most ammo reserves were shaved compared to their ''Half-Life'' counterparts. This really hurts the Python and Crossbow the most, reducing Gordon's carrying capacity of the latter to a mere ''two'' spare magazines. It also doesn't help that ammo pickups for these weapons provide ''two'' magazines worth of ammo, reaching the ammo cap instantly and making it highly likely for any additional ammo boxes to just be left behind.

** Thankfully, this one is to the player's advantage: Black Ops Assassins don't retain their insane damage or firing rate from ''Half-Life''. They also retreat to hide more often, backing away when too much damage is done, and aren't as fast as they were, despite the higher jumps they can do. Even when they become cloaked on Hard mode, they're easier to track down by the lights of their goggles (see LaserSight above).
** HECU snipers now fire much slower and have a visible red beam, making them easier to see and avoid, and don't murder you in two hits. However, they ''must'' be taken out with explosives; simply shooting the "figure" representing them doesn't work at all.

* NintendoHard: This game is considerably more difficult than ''Half-Life''. For starters, the Tentacles in "Blast Pit" are ''far'' more sensitive to noise this time around (which most likely has to to with an eye on top of their tentacle, as pointed out by a research note on one of the boards), the HECU's firing rate is no longer restricted to burst-firing, now eating up your health like a cocaine addict with crack, Barnacles can take ''four'' crowbar whacks instead of one in the series' official games so you're forced to engage them from a distance and actually use ammo, and the Vortigaunts, in addition to using basic squad tactics, charge up their attacks at the speed of ''Half-Life'''s hard mode (read: almost instantly), and can actually take a few hits before dropping. Even the ''headcrabs'' react a bit faster than average. On top of that, all enemies became smarter than their original selves; see ArtificialBrilliance for more details.

** There's one you can get an achievement for: If you decide not to push in the specimen and wait long enough, the scientists in the room will yell out [[https://www.youtube.com/watch?v=iitFrs5-TYQ&t=1m20s "He waited too long! We can't contain it!"]]

** Notably, the giant fan in "Blast Pit" is both even more unsafe ''and'' lethal; not only is the switch to activate it placed on the opposite side of where the ladder is situated (instead of directly in front of the ladder as in the original), but the cutout for said ladder is not deep enough to keep you safe from the fan blades once they start spinning.
** On the whole though, considering that the original ''Half-Life'' could be considered a TropeCodifier for its lack of OSHA compliance, ''Black Mesa'' has had a lot of thought put into making the place look like an operating government facility rather than a collection of safety hazards. Notable are the number of fire extinguishers available... none of which can be actually grabbed and used to put out a fire.

*** The iconic Crowbar doesn't appear until Gordon enters through the vent in the Sector C lobby to find it holding a pair of doors shut. To compensate for this, the areas prior focus on utilising enemy-igniting emergency flares and an accompanying Security Guard in order to clear out the zombie-infested hallways.
*** The Glock-17 Pistol isn't scavenged off the dead security guard that was originally blocking the entrance to the Sector B Coolant Reserve. Instead, the first opportunity to get the pistol is in the locked Coolant Reserve security office that requires a scientist to open, which also nets you a few Mk 2 Grenades like in ''Half-Life''. This would be changed in the ''Definitive'' update of the game, where it once again appears just before the Sector B Coolant Reserve (you still can't get the still alive guard in Sector C killed and get the pistol early that way).

*** In Early Access, the SPAS-12 Shotgun wasn't available until "We've Got Hostiles", which is a whole chapter later than it originally debuted in "Office Complex". The first shotgun that Gordon could obtain was wielded by one of the HECU soldiers that guards the elevator up to the surface. This was rectified in the public release. The only minor difference being that the player needs to save the security guard that opens the fenced storage area to reach the shotgun stored within it rather than the gun just being on a box outside of the fenced area.

** The ''Surface Tension: Uncut'' update for the 2015 retail release deserves special mention here. Not only is all of the marine dialogue re-recorded and expanded upon, but there are several setpiece battles and sections that don't even appear in the original recursive mod.

*** It's only at the end of the "Xen" chapter do you reach that all too familiar island, and even then, it has a significant number of changes that make it a far cry from its ''Half-Life'' appearance. For starters, you don't arrive from a set of moving platforms floating above the island. Rather, you enter it from the side by crossing twisted bridges of knotted roots. While the exterior is still guarded by hanging alien turrets and packs of Houndeyes, the interior has received a drastic overhaul; the waterlogged room with the barest pretence of a puzzle is now replaced by a snaking network of smooth tunnels, linking to rooms containing three beam emitters and a control room, all made from a never-before-seen technology; too alien be human, too organic to be Combine. This network becomes the centrepiece of a series of puzzles, as you navigate through the islands interior and exterior in order to repair the damaged teleporter generator, socket-switching and hunting around for Xen crystals to power its components. To sum it all up, it's basically a revamp of the Citadel core puzzle from ''[[VideoGame/HalfLife2 Half-Life 2: Episode One]]''.
*** Large stretches of "Gonarch's Lair" don't actually involve fighting the titular testicle monster. In some instances, you have to [[spoiler:run away from it, similar to Antlion Guardian chase sequences of ''Half-Life 2: Episode 2'']]. The course of action that the player is intended to take is almost always visually implied through both the environment and the Gonarch's placement during these sequences. As for the chapter itself, the copious amounts of webbing coating the environment combined the overabundance of Headcrabs compared to other wildlife really lends credence to this chapter's islands being part of a single, enormous nest, with the Headhumper queen herself as its sole, hyper-aggressive defender.
*** Like the other Xen levels, "Interloper" has been entirely revamped, only retaining the base concepts that made up the original chapter. Since the exploration of Xen was greatly expanded upon in the previous two levels, the first two maps of the original "Interloper" that had you exploring floating islands of the borderworld have basically been cut out to the point that only a tweaked version of the Tentacle section from the second map remains. In addition, there's still the Gargantua encounter, but it's now been turned into a chase sequence where you speed your way through [[spoiler:a home of multiple Gargantuas all trying to kill you until you escape the area]]. The encounter with the friendly Vortigaunts is still there, but the area they're located has been transformed into an impoverished slum that needs to be traversed. Finally, the Alien Grunt factory still caps off the level, but the layout to get through it has been entirely revamped. Some examples include the factory's barrel conveyor belt section being vastly extended, and the socket-switching puzzles seen in "Xen" make a return at several points throughout the factory. The purpose of Gordon going through the factory has also changed where instead of just needing to find your way through it, the player now goes about changing or breaking certain things to outright destroy the factory. Finally, the elevator climb at the end of the level still exists, but instead of being a bunch of annoying spinning elevator platforms, it's been turned into [[spoiler:a single ClimacticElevatorRide fighting off a horde of Alien Controllers until you reach the top to take the portal to the FinalBoss]].
*** While on the topic of "Interloper", the revamped chapter [[spoiler:also introduces a new type of helpful crystal once you've made it to the Alien Grunt factory. You start to come across green crystals that continuously restore the Depleted Uranium-235 ammo needed for the Tau Cannon and Gluon Gun; meaning that as long as you remain near such crystals, you will have infinite ammo to spam the usage of said guns. This was most likely done to parallel the use of the supercharged Gravity Gun in the final levels of ''VideoGame/HalfLife2'' where Gordon goes ham on his enemies non-stop with his most powerful weapons]].
*** "Nihilanth" forgoes its namesake final boss teleporting you periodically as one of his attacks. This half-mechanical alien overlord has better resolve this time around and is more focused on ''killing you'' instead. And while he still has the power to teleport things, he'll now use it to [[spoiler:throw cars and building fragments at you]].

* OneManArmy: Like in the original ''Half-Life'', Gordon Freeman became one over the course of the game thanks to his wits, his HEV suit and an incredible collection of mundane and exotic weapons he picked up along the way. By the end of the game he would have had massacred his way through two armies, survived an incredibly hostile alien world, and capped it off by taking on and killing a being which was for all intents and purposes an [[EldritchAbomination alien]] [[PhysicalGod god]]. Did we mention that [[BrickJoke he may not had been wearing a helmet]] through all of it?

** The Hivehand weapon, now more gross than ever. Gordon has to AssShove his hand into the poor creature in order to use it.

* {{Retirony}}: The male scientist in the Anomalous Materials lab that lampshades the ArtificialAtmosphericActions he's taking remarks that he'll check with office about how many vacation days he's gotten during his work for 25 years, with the implication he'll use them as soon as the test concludes. Given that the Resonance Cascade happens shortly after, and humanity gets enslaved by the Combine after that, it's highly unlikely that he'll get to have even a minute off.

** In "Unforeseen Consequences", as the elevator plummets to the bottom of the shaft, you can throw a physics object through the glass, allowing the player to climb up the emergency ladder a little earlier then the player is supposed to. The elevator still falls, but provided that you loaded the next section in before it is destroyed, the scientists would be alive and well at the bottom of the shaft. You can also place the chair near the edge of the elevator platform before the elevator falls, which actually ''stops the thing from falling''. The scientists on the elevator will still be stuck in their "scared" poses though.

** During "Surface Tension", prior to entering the Laser Tripmine warehouse, there's a scene where you witness a scientist run out of a nearby structure to help a security guard downed by a HECU sniper in the area. A few moments later, the sniper would then kill the scientist as he tries to help the security guard. If you kill the sniper before he shoots the scientist however, the scientist remains on the field forever kneeling before the now dead security guard. This was fixed in the 2015 retail release; after the sniper is killed, the scientist will become startled, run into the nearby minefield, and die anyway.

** In the same chapter, the guard that rushes the Tentacles [[LeeroyJenkins is literally named Leeroy Jenkins]].

*** As part of a set of whiteboard scribblings about a budget debate, questions are raised about Lab A's high pizza budget. Four questions are bulleted out: "Why?" "What are they hiding?" "What does the book tell them?" "What does it fail to tell us?" - the questions Vogel demands of Henry Jones regarding the Grail diary in ''Film/IndianaJonesAndTheLastCrusade''.

** When fighting HECU Marines, Black Mesa Security guards might call them [[Series/GomerPyleUSMC Gomer]].
** A piece of paper taped to a wall in Xen shows the expedition's kill tallies of various alien creatures. Houndeyes are nicknamed "[[Franchise/SonicTheHedgehog Sonic the Bull Dog]]" and [[spoiler:fire Houndeyes]] are called "[[WesternAnimation/TheSimpsons Mr. Burns]]".

** The HECU's vehicular lineup is more consistent with what the U.S. Marines would use (M2 Bradleys and F-16s from the original are replaced with LAV-25s and AV-8B Harrier [=IIs=], respectively), they correctly refer to their medics as "corpsmen" and their first aid kits as [=IFAKs=][[note]]Individual First Aid Kits[[/note]] in the retail release, and they use protective gear modeled after real-world equipment including the [[https://web.archive.org/web/20130618122028/http://i146.photobucket.com/albums/r261/ArvinPabico/armorvest-Crye-armor-7.jpg Crye Precision Armor Chassis]] and the [[https://web.archive.org/web/20160327140300/http://wwww.specwargear.com/retro/images/helmet-CCT%20IBH-1.jpg Integrated Ballistic Helmet]].

* SideBet: A scientist and security guard in the Anomalous Materials lab happen to be betting their lunch on whether Gordon will show up to work. If you walk in on them, the guard will gloat about having won the bet.

* SlaveryIsASpecialKindOfEvil: As in the original game, the Vortigaunts are also known as Alien Slaves, but their plight is much more explicitly sympathetic this time around. Once on Xen, the first time a player encounters Alien Grunts and Vortigaunts there, the former is savagely beating one of the latter for being too sick to work quickly while other Vortigaunts look on in fear and sorrow. Later on Alien Controllers will torture Vortigaunts via psychic means into attacking the player; [[spoiler:if the player kills the Controllers first, the Vortigaunts will stop attacking.]] In the Alien Grunt factory, Vortigaunt bodies occasionally pop up as a result of the incredibly poor working conditions they're forced to operate in.

* SniperScopeGlint: HECU Snipers' sniper rifles have a built-in LaserSight that doubles as this, which disappears momentarily when they fire a shot. This is contrast to the original game, where enemy sniper's were only given away by the silhouette of their rifles.

** Many [=NPCs=] that were normally done for without split-second reaction times are now far easier to save due to equal parts changes in script pacing and muscle memory.
** Zigzagged in "Surface Tension". In the ''Surface Tension: Uncut'' mod, the player come across a security guard who, like in the original ''Half-Life'', needs to be escorted to unlock a door. In ''Half-Life'' this guard most likely ends up getting killed as he would follow the player (unless told not to) into the car park and [[SuicidalOverconfidence pick an unwinnable fight with the resident Gargantua]]. In the mod ''Surface Tension: Uncut'', the guard is unable to follow the player as they enter the car park via an air duct he can't climb through, so he just wishes the player good luck. Come the ''Surface Tension: Uncut'' Update which implements the mod into the retail game proper, [[spoiler:the guard never enters the parking lot as, just after he has unlocked the door for the player, an Alien Grunt teleports in behind the guard and the door locks behind the player. [[SoundOnlyDeath The ultimate fate of the guard is just heard from behind the locked door, as he is savagely beaten to death by the Alien Grunt]].]]

* StuffBlowingUp: There's several new explosive setpieces in "Surface Tension" involving fuel trucks. One is blown up by Vortigaunts and takes a grounded Osprey with it, while another is used by HECU soldiers to set a trap for a Gargantua... [[NoSell to no effect]].

** Just before the final push to the Nihilanth, there's a large Xen healing pool with a charging crystal inside, allowing you to top off your health and energy before the final fight. The game does ''a lot'' to make it clear before hand that [[TheVeryDefinitelyFinalDungeon this is it]], though, so it isn't much of a surprise.

** One of the guards asks for help from Gordon with one of those critters, who apparently got onto his buddy's head and are making him act all weird. Right on cue, guess who walks out. The guard then proceeds to talk to his "buddy" as if he's all fine and well. You can guess how that ends.[[note]]If you kill the zombie before it gets him, though, you'll get access to the [[HandCannon .357 Colt Python]]/[[ShotgunsAreJustBetter SPAS-12 Shotgun]] much earlier than normal. His reaction seems to lean way towards being shell shocked, thanking you when you kill his "buddy".[[/note]]

** Despite a scientist's warnings on the Tau cannon's instability, a careless security guard still manages to overcharge the gun, killing them both. The scientist was reduced to bite-sized chunks, and there was nothing left of the guard but a ''[[SmolderingShoes smouldering pair of boots]]''.[[note]]You get an achievement for [[ViolationOfCommonSense doing the same thing yourself, though you (if at full health) won't explode.]][[/note]]
* TookALevelInJerkass: Some of the scientists and guards starting from "Anomalous Materials" are now short-tempered, egotistical, grumpy, or all three. Like Hunter, the guard who greets you with a sour disposition once you finally reach Level A of the Lambda Reactor Core. At least after the Resonance Cascade, a scientist in Lambda Complex [[LampshadeHanging noted this]] and figured this is in part due to everyone is under a lot of pressure trying to survive and working feverishly under desperate circumstances to reverse the disaster.
* TruthInTelevision: The hand grenades have a noticeable trail of smoke and sparks when thrown. While this could be a gameplay conceit for players in place of the blinking red light of ''VideoGame/HalfLife2'', earlier Mk. 2 grenades did have fuses that sparked after being lit... Which brings into question why they're not only using outdated grenades but ones with outdated fuses as well.

* UnusableEnemyEquipment: HECU marines who wield rocket launchers are introduced fairly early on, but the weapon disappears altogether after they fire a single shot or get killed, preventing you from picking it up. The rocket launcher remain off-limits until you come across one in "Surface Tension".
* UpdatedRerelease: The Steam release of the game, released in 2015, is effectively this on account of receiving ''a lot'' of improvements such as new models/sounds/animations/voicelines, [[PlayerVersusPlayer PvP multiplayer]] and the final four Xen chapters.

** You can lure soldiers in one of the labs and kill them with Emergency Tesla Discharge, which disintegrates them completely.

* WelcomeToCorneria: Some of the friendly NPC dialogue to each other, outside of scripted events doesn't match up, or turns into unusual cases of DeadpanSnarker.

Following the completion of the original game, work is not quite done yet for ''Black Mesa''. In February 2021, a FanRemake mod for ''VideoGame/HalfLifeBlueShift'' was announced, and is being developed by the HECU Collective team. As of December 2022, the first four chapters of ''VideoGame/BlackMesaBlueShift'' have been completed.

** Speaking of the Crossbow, it's drawback animation can no longer be cancelled by switching to another weapon. Using its scope also takes a bit more time.

* ActionSurvivor: Much more pronounced for most Black Mesa personnel (Including Freeman) in ''Black Mesa'' than in ''Half-Life'' between the fact most enemies had become more dangerous and all Black Mesa characters having more chances to shine. Under the right circumstances some security guards can take on whole squads of Xen monsters and HECU marines and win, and even the normally defenceless scientists got a few moments such as one who took out a Headcrab by smashing it with an old computer monitor.

* HyperactiveMetabolism: Drinks from the vending machine can heal you, with each can equating to 1 HP. You can either have the machine dispense one drink at a time by pressing its buttons, or, if you're impatient, just smack it with a crowbar and let the cans spew out.

* HyperactiveMetabolism: Drinks from the vending machine can heal you, with each can equating to 1 HP. You can either press the buttons on it and get one drink at a time, or, if you're impatient, just smack it with a crowbar and let the cans spew out.

* EasilyThwartedAlienInvasion: Subverted. Like in the original Half Life, while the HECU managed to contain the extra-universal alien incursions at first, as time goes on the AlienInvasion becomes more organised and coordinated, leading to the HECU gradually losing ground and the fighting increasingly desperate as they are overwhelmed by both sheer numbers and powerful alien soldiers and machinery/monsters like the Grunts and the Xen Manta Rays. The situation gets bad enough that by ''"Surface Tension"'' and ''"Forget About Freeman"'' the US government had issued an evacuation warning for the ''entire state of New Mexico'' as the HECU retreats in utter rout, showing how badly shit has hit the fan.

** The presence of several marines and a tank outside the Lambda Complex goes unexplained in the original game. Here, they're part of a convoy trying to fleeing Black Mesa after the order to pull out is given, and are forced to fight Freeman after an Alien Aircraft destroys their exit.

* AdaptationalExplanation: There's now a justification provided for why the two soldiers who capture Gordon and throw him into a trash compactor [[WhyDontYouJustShootHim don't bother making sure he's dead]]. They're shown to have been attacked by headcrabs before they could ensure Gordon's demise in the compactor, with one zombified and the other reduced to meaty chunks, presumably having panicked and blown himself up with a grenade.
* AdaptationalContextChange: The final HECU encounter on the surface in "Forget About Freeman!" is never given much context in canon, but presumed to be a token force guarding the entrance to the Lambda Complex. Here, it's a full on LastStand for the HECU, as an alien craft destroys a convoy trying to flee the facility, forcing the remaining marines and a lone tank to dig in against Gordon. Accentuating this is a trio of Ospreys fleeing the facility while helicopters and jets dogfight with alien craft.

* WeAllLiveInAmerica:
** Despite the New Mexico setting, the vending machines are stocked with BrandX versions of brand-name British and European snacks like Walker's, Maltesers, and (the British version of) Smarties. The digital readout on the machine itself says "Feeling peckish?" which is not an expression Americans use.
** There's also a [[Series/ChuckleVision Chuckle Brothers]] mug in some of the offices, though only in the original mod release.
** Some of the facility's signage uses British terms and spelling, such as "authorised" instead of "authorized".

* WhoForgotTheLights: The resonance cascade was not kind to the Black Mesa Research Facility's lighting systems. In many locations, the lights are burned out or lacking power, some even more so than in ''Half-Life''. To make up for it, the HEV suit has an InfiniteFlashlight installed.

** There's a workshop in Black Mesa with a [=DeWALT=] chop saw with a [="DeWOOT"=] logo.

** The added detail available from the new Source engine allows for unprecedented levels of gore in Black Mesa. Along with the usual blood splatters from kills, almost every enemy can be gibbed by explosions or especially powerful weapons, while blood (both human and alien) and Bullsquid acid will regularly splash on Gordon's arms and weapon in disturbing detail should he be injured, attack an enemy up close, or get caught in an enemy's gibbing.[[note]]This is disabled by default in the retail release due to an unresolved lag spike when the effect first occurs, but can be re-enabled with console command '''cl_mdldetailfx_enable 1'''.[[/note]] Dismembered body parts also litter Black Mesa.

** At the start of "Unforeseen Consequences", a scientist can be seen performing CPR on a security guard, and upon waiting about 30 seconds, the CPR is successful and the guard wakes up; in Black Mesa however, the guard's body is more bloodied, and the scientist's CPR never seems to succeed.

** In ''Power Up'', you could escape the Gargantua in the first game through a door while he was distracted with killing HECU marines, and it would forget about you until you wandered in again. Not this time. The monster goes right to the door you went through after its killing spree and ''actually reaches in with his flamethrowers'' if you're near it. Suffice to say, a lot of players [[StealthPun got burned]] by that one unexpectedly.

** [[https://www.youtube.com/watch?v=Mb9Qw3sLwKs [=HEV=] zombies' suits repeatedly provide distorted status readouts,]] as if the suits are having a hard time comprehending their users' zombified state.

* EleventhHourSuperPower: Towards the middle of "Interloper", you will come across large green crystals that [[spoiler:quickly replenish your supply of Depleted Uranium-235, giving you unlimited usage of the Tau Cannon and Gluon Gun]].

** As in Half-Life 2, Headcrabs now have a chance of surviving the death of their Zombie host to continue attacking Freeman, unless said Zombie was killed via headshot.

*** The Colt Python was available ''significantly'' earlier than it was in ''Half-Life'' - previously, it couldn't be found until you defeated the Tentacles in "Blast Pit". In Early Access betas, it could be obtained in "Office Complex" at the location where you would've normally first obtained the SPAS-12. In the public release, it was moved back to where it was originally found in Half-life, with the SPAS-12 taking its place.

* SatchelCharge: The Satchel Charge functions in pretty much the same way it did back in Half-Life 1, being a bag of explosives triggered by a remote detonator. This time around, satchels are thrown with the primary fire button and can be picked up by the player in case they dropped the satchel prematurely. The secondary fire button, meanwhile, detonates the satchel.

* ZeroToHero: Like in the original Half-Life, Black Mesa chronicles Gordon Freeman's transformation over the course of the game from a hapless civilian scientist trapped in the middle of a nightmarish disaster he unwittingly helped cause, to a cunning and lethal OneManArmy who fought his way through entire armies, monsters, and an entire extradimensional DeathWorld to end the Resonance Cascade and save the Earth from an AlienInvasion.

* UnusableEnemyEquipment: HECU soldiers who wield rocket launchers are introduced fairly early on, but the weapon disappears altogether after they fire a single shot or get killed, preventing you from picking it up. The rocket launcher remain off-limits until you come across one in "Surface Tension".

* ActionSurvivor: Much more pronounced for most Black Mesa personnel (Including Freeman) in ''Black Mesa'' than in ''Half-Life'' between the fact most enemies had become more dangerous and all Black Mesa characters having more chances to shine. Under the right circumstances some security guards can take on whole squads of Xen monsters and HECU soldiers and win, and even the normally defenceless scientists got a few moments such as one who took out a Headcrab by smashing it with an old computer monitor.

* AlasPoorVillain: Compared to their ''Half-Life'' depictions (where they were no more than additional {{Mooks}} to shoot at), ''Black Mesa'', especially the Steam release, will make you feel sorry for the HECU Marines once the tide is turned against them. Of particular note is one heartbreaking conversation between a mortally wounded soldier and a corpsman heard on the radio near the conclusion of "Surface Tension".

* ArmiesAreEvil: Downplayed from the original game. While the Hazardous Environment Combat Unit retain all of their villainous intentions from the source material, they're more humanized in this game, and various radio transmissions heard throughout "Surface Tension" only serve to further elicit sympathy towards these soldiers as they're increasingly overwhelmed by the invading Xen forces.

* AdaptationalContextChange: The final HECU encounter on the surface in "Forget About Freeman!" is never given much context in canon, but presumed to be a token force guarding the entrance to the Lambda Complex. Here, it's a full on LastStand for the HECU, as an alien craft destroys a convoy trying to flee the facility, forcing the remaining soldiers and surviving tank to dig in against Gordon. Accentuating this is a trio of ospreys fleeing the facility while helicopters and jets dogfight with alien craft.

** The HECU is given a couple of moments to make the player empathize with them, such as a wounded marine being given triage instructions by a medic over radio, only to expire mid-conversation. Another scene has two soldiers wonder why they are even fighting here, with one admitting it feels wrong to gun down scientists who won't fight back. Finally, the last major surface battle has the HECU desperately trying to retreat from the facility, with those that fight Gordon becoming trapped after an alien craft fries all of their vehicles except a tank (which can't clear out the wrecks, leaving it trapped in the area as well).

* ArtificialStupidity: HECU soldiers in the mod release, as well as earlier versions of the retail release, were notorious for their tendency to either stand in one place while shooting the player or blindly rush forward without any semblance of tactics. This was rectified in later updates to the retail game by a complete overhaul of the soldiers' AI.

** Many of the other Black Mesa [=NPCs=] who survive more than two minutes of their debut also qualify, from security guards who do their best to fight off the aliens and HECU soldiers to protect the scientists, to HECU troops who, when not trying to silence all witnesses, are fighting tooth-and-nail against an AlienInvasion, to the scientists who are actively working to reverse the Resonance Cascade despite the near-impossible circumstances and the mortal danger they find themselves in. The security guards and scientists in particular proved to be immense help for Gordon Freeman as he fought his way through Black Mesa to get help at the Lambda Complex.

* CombatMedic: [[ShownTheirWork Correctly called "corpsmen" in this game]], these are a new class of HECU Marine carried over from ''VideoGame/HalfLifeOpposingForce''. Like their predecessors, they will heal fellow HECU Marines should they get wounded in the field. Unlike their predecessors, the corpsmen are armed with the same weapons as regular HECU Marines ([=MP5s=] and SPAS-12s as opposed to Glock 17s), and are just as competent as them.

** The brutality of the Gargantua's flame attack against [=NPCs=] in the original, seen with the HECU soldiers in "Power Up", was limited to gibbing. In the same chapter of this game, you'll actually see them set alight by the flames, causing them to flail and scream as they burn to death.

** The soldier who throws a satchel charge into a pipe while Gordon is climbing through it gets crushed when the resulting explosion blows the pipe's access hatch off its hinges.

** The soldier broadcasting orders over the radio to evacuate the facility in "Forget About Freeman" [[UncertainDoom might be]] a case of this, as he's heard yelling "DOWN, DOWN!" just before an explosion causes the transmission to cut out.

* DumbMuscle: Consistent with the misspelled threatening graffiti in the original, there's an exchange between two soldiers in the lobby in "Questionable Ethics" where one of them tries to read the Latin motto on the wall, is told that it's Latin, and then grumbles dismissively about [[GlobalIgnorance "foreigners"]].

* EasilyThwartedAlienInvasion: Subverted HARD. Like in the original Half Life, while the HECU managed to contain the extra-universal alien incursions at first, as time goes on the AlienInvasion becomes more organised and coordinated, leading to the HECU gradually losing ground and the fighting increasingly desperate as they are overwhelmed by both sheer numbers and powerful alien soldiers and machinery/monsters like the Grunts and the Xen Manta Rays. The situation gets bad enough that by ''"Surface Tension"'' and ''"Forget About Freeman"'' the US government had issued an evacuation warning for the ''entire state of New Mexico'' as the HECU retreats in utter rout, showing how badly shit has hit the fan.

*** The HECU soldiers borrow the AI and animations of the Combine soldiers, albeit with the AI rewritten to make them even more competent. This allows them to shoot while standing and on the move, among other things.

* GasMaskMooks: HECU Grunts, who make up the majority of the soldiers encountered throughout the game, all wear gas masks.

** HECU Snipers now fire much slower and have a visible red beam, making them easier to see and avoid, and don't murder you in two hits. However, they ''must'' be taken out with explosives; simply shooting the "figure" representing them doesn't work at all.

* RadioVoice: HECU soldiers who wear gas masks have radio filters over their voices.

** The final surface portion of the original (set at the end of "Forget About Freeman!") consisted of the player fighting a pair of HECU troopers and a tank. In the mod version, the soldiers are more numerous, a trio of ospreys is fleeing the base, and several alien aircraft are engaging Apache gunships and jet fighters in battle. In the release version, [[SerialEscalation the HECU has several vehicles, but all but the tank are destroyed by an alien aircraft]].

** Think Snarks are bad? In Xen, there are locations where their nests are ''everywhere'', and you can find yourself falling into a pit full of them after falling into and breaking several webbing-suspended nests which overed the opening

* EmpathicEnvironment: The light and time of day in "Surface Tension" correspond to the strength of the HECU forces the playe encounters in the level and their effectiveness wanes, the sun makes its way down the horizon. Tellingly, the HECU's retreat from Black Mesa in "Forget About Freeman!" happens at sundown, with their defeat symbolically representing mankind's coming loss against both the Xen Invaders and the Combine.

---> '''Scientist:''' [[ExactWords If another instrument malfunctions today, I'm going to explode!]]

** In ''Half-Life 2'', Barney's first line concerns the beer he owes Gordon, a reference to the pre-disaster security guard dialogue about sharing a beer with Gordon after work. But these lines aren't said by Barney, who is canonically the guard originally seen at the start of the tram ride, and could not have made it to the Sector C labs before Gordon. This is rectified by instead having the guard at the Sector C tram station reference the fact that Barney's bar tab is past due and that he relies on others to buy drinks for him.
*** Of note is that the original dialogue about sharing a beer is still in this game, albeit slightly changed:
---->"Hey, catch me later. You, me, and Calhoun will go out and get that beer he owes ya."

* LastStand: The final surface battle in "Forget About Freeman!" has been converted into one for the HECU. As Ospreys flee overhead amidst jets and helicopters dogfighting alien craft, an HECU convoy on the ground tries to flee, only for the majority of their vehicles to be zapped by an alien craft as Gordon emerges from underground. The survivors engage him in battle, only to be cutdown.

** The Black Ops female assassins appear to be wearing modified, all-black [[VideoGame/{{Portal2}} Long Fall Boots]], which explains how they can jump around without breaking their legs. It's also rather funny when you realize that not only are the military trying to eliminate the Black Mesa Research Facility, they're doing so with gear from the company's primary competitor.
*** Also notable is that the boot's predecessors, the [[VideoGame/{{Portal}} Advanced Knee Replacements]], were a recycled prop from WhatCouldHaveBeen the Black Ops' successor in ''Half-Life 2'', the female Combine Assassin. What's more, Assassins now dual wield pistols, another trait they share with their cut descendants. In the original game, they had only one.

** On the whole though, considering that the original ''Half-Life'' could be considered a TropeCodifier for its lack of OSHA compliance, ''Black Mesa'' has had a lot of thought put into making the place look like an operating government facility rather than a collection of safety hazards.
*** Notable are the number of fire extinguishers available... none of which can be actually grabbed and used to put out a fire.

** Zigzagged in "Surface Tension". In the ''Surface Tension: Uncut'' mod, the player come across a security guard who, like in the original ''Half-Life'', needs to be escorted to unlock a door. In ''Half-Life'' this guard most likely ends up getting killed as he would follow the player (unless told not to) into the car park and [[SuicidalOverconfidence pick an unwinnable fight with the resident Gargantua]]. In the mod ''Surface Tension: Uncut'', the guard is unable to follow the player as they enter the car park via an air duct he can't climb through, so he just wishes the player good luck. Come the ''Surface Tension: Uncut'' Update which implements the mod into the retail game proper, [[spoiler:the guard never enters the car park as, just after he has unlocked the door for the player, an Alien Grunt teleports in behind the guard and the door locks behind the player. [[SoundOnlyDeath The ultimate fate of the guard is just heard from behind the locked door, as he is savagely beaten to death by the Alien Grunt]].]]

* UnusableEnemyEquipment: HECU soldiers who wield rocket launchers are introduced fairly early on, but the weapon disappears altogether after they fire a single shot or get killed, preventing you from picking it up. The rocket launcher remains off-limits until you come across one in "Surface Tension".

* ClassicVideoGameScrewYous: Shortly after getting a crowbar, you have to smash through a pile of rubble. One dev thought it would be funny to place [[ExplosiveBarrels an explosive crate]] there.