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[[caption-width-right:350:A tense moment for Gordon Freeman, thirty seconds before blasting an alien's skull off.]]

->''Run. Think. Shoot. Live.''

''Half-Life'', by developer team Creator/{{Valve|Software}} and originally published by Creator/{{Sierra}} in its final years, is the first in the ''VideoGame/HalfLife'' series and follows a day in the life of physicist Gordon Freeman, a bearded, bespectacled HeroicMime who works in the Anomalous Materials laboratory at the vast Black Mesa Research Facility, a [[ElaborateUnderGroundBase top-secret complex]] in the middle of the UsefulNotes/NewMexico desert. While performing a test on a [[GreenRocks strange crystalline substance]], Gordon accidentally initiates a '[[NegativeSpaceWedgie resonance]] [[TechnoBabble cascade]]' -- an event which causes bizarre, violent creatures to be spontaneously transported from {{another dimension}}. Now Gordon must work his way across the base in pursuit of a way to close the dimensional rift, fighting off not only the acid-spewing, electricity-shooting, zombifying aliens but also the Hazardous Environment Combat Unit (HECU), a special unit under the [[ArmiesAreEvil US military]], who have swarmed into the complex and are destroying the creatures and silencing the facility's personnel with equal vigor.

Notable for its total immersion of the player. The game is [[UnbrokenFirstPersonPerspective entirely played in first person]] and in real time, with very little sound not produced by actions in the game world, and no sounds at all made by the central character; also, there are few cutscenes (and even they let you look around during them) -- the player has control of the character at all times, and the story unfolds entirely in-game.

The designers actually had great difficulty with the level design at first, and got stuck in a rut. In order to take stock, they created a single level containing every gimmick, enemy, and bit of level furniture that they had come up with for the game so far. Said level was fantastic, and they realized that this density of [[VideogameSetPiece set pieces]] was the "certain something" the game lacked.

Creator/GearboxSoftware made three official {{Expansion Pack}}s for the original game, which act as {{POV Sequel}}s for the main plot. They are as follows:
* ''Opposing Force'' begins shortly after the Resonance Cascade, and has the player controlling Corporal Adrian Shepard, one of numerous US Marines sent as the initial clean-up team. Involved in a chopper crash and separated from his squadron, Shephard awakens as the Marines begin their evacuation. Notably fills in what happened in Black Mesa after Freeman takes the battle to Xen. Additionally, Shephard is the only protagonist whose fate still remains completely unknown.
* ''Blue Shift'' runs concurrently with about the first third of the main plot, with the player controlling security guard Barney Calhoun. Working to evacuate the facility following the accident, Barney's story examines the outbreak from a survivors perspective; instead of combating the problem like Freeman, it's about getting out alive. The only expansion (presumed) to be canonical, as Barney [[LateArrivalSpoiler later reappears]] as a significant supporting character in ''VideoGame/{{Half Life 2}}'' and its following episodes.
* ''Decay'' follows two other Black Mesa scientists, Drs. Gina Cross and Colette Green, and is the only official co-operative entry to date. Following the doctors as they act as key scientists, their story shows the work of the Lambda scientists that Freeman co-operates with, explaining how they acted to undo the Resonance Cascade and Xen invasion. Developed and released exclusively for the [=PS2=] version of ''Half-Life'', it can also be played on the PC thanks to the efforts of the mod community.

Gearbox took some liberties towards the storylines, which still causes [[BrokenBase fan disputes]] to their canonicity; as WordOfGod by the series' main writer, Marc Laidlaw, has deemed them [[LooseCanon semi-canonical]] until further notice, some label them as FanonDiscontinuity, while others ferociously defend their being canonical -- due in no small part to Adrian Shephard's status as an EnsembleDarkhorse.

The game engine was also famous for being highly customizable, leading to a long series of mods. Some of them were single-player, such as ''VideoGame/GunmanChronicles'' and ''VideoGame/TheyHunger'',[[note]]TheWestern and SurvivalHorror[=/=]ZombieApocalypse[[/note]] while famous multiplayer mods include ''Deathmatch Classic'', ''Ricochet'', ''Day of Defeat'' , ''Natural Selection'', ''VideoGame/TheHidden'' , and ''VideoGame/AfraidOfMonsters''.[[note]]Repectively: old school VideoGame/{{Quake}}-style combat; fast-paced VideoGame/QuakeIIIArena-style action; ''{{Tron}}''-esque energy disc battles, as you hop between platforms; a gritty World War II combat simulation; aliens vs. SpaceMarines, in a cross between first person shooter and real time strategy; SurvivalHorror[=/=]StealthBasedGame; and SurvivalHorror[=/=]StealthBasedGame.[[/note]] Especially notable of all mods are ''VideoGame/{{Team Fortress|Classic}}'' and ''VideoGame/CounterStrike'', both of which have famously ascended to independent games in their own right (and adopted by Valve themselves); because of this, Half-Life and its mods are collectively one of the most influential games of all time.

A sequel, ''VideoGame/HalfLife2'', which would prove no less influential, was released in 2004.

In September 2012, ''VideoGame/BlackMesa'', a comprehensive FanRemake that recreates the entire game in the Source engine, was released, after over [[ScheduleSlip eight years]] [[VaporWare of waiting]].

In early 2013, with Valve's push to get Steam on Linux, they ported ''Half-Life 1'' to [[UsefulNotes/{{UNIX}} Linux]], as well as UsefulNotes/MacOS.

If you enjoyed this game, or want to watch it instead of play it, do check out Machinima/FreemansMind.
!!Half-Life contains examples of:

* ActionGirl: Drs. Gina Cross and Colette Green.
* ActionSurvivor: Dr. Gordon Freeman and Barney Calhoun, the latter especially. Both men spend a lot of their time trying not to get killed by the aliens and the [=HECU=] forces but where as Gordon becomes an ActionHero, Barney's story is all about getting out of Black Mesa alive and not having to risk his life for extra reasons outside of his control.
* AirVentPassageway: While the series as a whole is famous for it, one of the most memorable subversions happens in the original. You are forced to crawl through some air vents, but the Marines hear you and shoot the hell out of it. The entire vent falls off the ceiling and crashes to the ground with you inside, or if you backed up, trapped in another part of the vent with the Marines shooting the hell out of you, albeit with more cover.
* AdjustableCensorship: You have the option to disable the blood and/or gore.
* {{Area 51}}: Black Mesa is basically a civilian-owned expy for this.
* ArtificialBrilliance:
** ''Half-Life'' was widely praised for the A.I. of its human Marine enemies, who were the first FPS enemies to work in squads and use complex tactical behaviors and movement patterns instead of simply charging in a straight line at the player...
** The cockroaches are also [[https://www.youtube.com/watch?v=Elwb2lV88hM pretty impressively programmed]] for prop [=NPCs=].
* ArtificialStupidity: ...of course, it still is not perfect. Grunts have a tendency towards friendly casualties when throwing grenades, and will forget about armed grenades they drop if they catch sight of the player. The player can also trick grunts into a killbox by lying in wait behind a corner. No matter how many of their fellow grunts are slaughtered, they will still charge blindly around corners.
** The player can actually do that with every enemy if there's a corner for the player to hide behind, making the Vortigaunt and Houndeyes very easy to pick off.
** Friendly [=NPC=]s have a tendency to get lost, stuck in rooms, refuse to follow you after a while and shoot you in the back. ''Opposing Force'''s HECU Marines in particular suffer from this quite badly at times, forcing you to double back if you need them.
* AttackItsWeakPoint: [[SarcasmMode Gee, I wonder why a gaping hole with a glowing purple orb inside just opened up on that giant monster.]]
* AwesomeButImpractical: The Gluon Gun can destroy any non-boss [=NPC=] in a second or so max. It also chews up all of your ammo in mere seconds.
* BadassArmy: The HECU. Made up of highly trained marines backed by a full repertoire of US military hardware. They're quite deadly, but unfortunately for them they're a single special forces battalion going up against an entire alien army (and [[BadassBookworm Gordon]] [[OneManArmy Freeman]]). Things go well for them at first, but once the alien invasion really gets underway they're rather quickly overwhelmed and resort to [[ScrewThisImOuttaHere pulling out of the facility altogether]].
** The Xen aliens get a mention too. They have a rather large number of [[CannonFodder easily killed mooks]], but the elite of their army ([[EliteMook alien grunts]] and [[TheJuggernaut gargantuas]] come to mind) are quite dangerous. Their 'aircraft' (another alien species) also seem to be a credible threat to fighter jets and helicopters (they were doing airdrops during Surface Tension, suggesting that the US military was unable to secure air superiority.)
** Not to mention the Black Ops. Compared to the HECU, they have access to the same equipment, but are also far better trained and specialized. And they do a much better job at handling both the Xen and Race X invasions, managing to be on equal footing with them for a while longer. Like the HECU, however, they're eventually overwhelmed as well and resort to [[ItsTheOnlyWayToBeSure nuking the facility]].
** Race X's aliens. Their [[EliteMooks Shock Troopers]] are arguably tougher to take down than the Alien Grunts, and their [[GiantMook Pit Worms and Gene Worms]] are shown to be just as tough, if not tougher, than the Gargantuas.
* BeeBeeGun: The Hornet Gun.
* {{BFG}}: The Displacer from ''Opposing Force'' is very obviously inspired by the trope namer.
* {{Bookends}}: The game begins and ends in a tram. ''Opposing Force'' matches this by beginning and ending in a military transport aircraft.
** Also, you go down an ''Manga/{{AKIRA}}''-esque lift at the end of ''Unforseen Consequences'' (the first chapter after the Resonance Cascade), and then down a similar one at the beginning of ''Lambda Core'' (the last chapter to take place at Black Mesa).
* BootstrappedTheme: [[https://www.youtube.com/watch?v=o5iUt1EtUqs Hazardous Environments]] is the music from the logo for Creator/ValveSoftware.
* BoringButPractical: The Hivehand, the only weapon you have that regenerates ammo. It's especially useful once you get to Xen, where ammo is very scarce overall.
* BossBattle:
** The original game had three; the [[PuzzleBoss Tentacle]], the [[DamageSpongeBoss Gonarch]], and the [[FinalBoss Nihilanth]].
** MiniBoss: The Gargantuas, tanks, and helicopters.
** ''Opposing Force'' had the [[PuzzleBoss Pitworm]] and the [[GiantSpaceFleaFromNowhere Geneworm]].
** Averted in ''Blue Shift'', which doesn't even have a FinalBoss.
* BossInMookClothing: Voltigores in ''Opposing Force''.
* CaptainObvious: In ''Opposing Force'' 's training level, Shephard gets shot point-blank with a shotgun to demonstrate the effectiveness of the PCV armor vest.
-->"[[DrillSergeantNasty As you can see, you are]] ''[[CrowningMomentOfFunny NOT dead]]''!"
* ContinuityNod:
** On the initial train journey, you pass by a security guard banging on a door; in ''Blue Shift'', where you play as a security guard, the first door you come to malfunctions, and if you look around while waiting for the guard on the other side to open it, you'll see Freeman passing you by. Later on, you can overhear some marines complaining about having to do the crap work because Shephard's team hasn't arrived yet.
** ''Opposing Force'' is full of them, being an {{Interquel}}, starting from the opening chopper ride (where you see the mountain pass Freeman navigates) to actually seeing Freeman enter the Xen portal!
* CouldntFindAPen: There are some numbers written in blood near a scientist's corpse in the chapter ''Lambda Complex.'' These numbers are a hint for an upcoming puzzle.
* CreatorCameo:
** Gabe Newell's office can be seen in the chapter "Office Complex".
** In "Pit Worm's Lair" where you have to press a button to eliminate a boss, you need to first enable a valve and a gearbox.
** In "Captive Freight" when you're traveling through the tunnels before reaching the train-yard, you will come across an opened box that just so happens to have gear shaped objects spilling onto the floor. Aka, a gearbox.
** In the fifth chapter of ''Opposing Force'' [[DeathByCameo there are two scientists lying dead near their desks]], which carry the nametags "S. Reardon" and "S. Jones", referencing Creator/GearboxSoftware developers Sean Reardon and Steven Jones.
* CreepyCockroach: Black Mesa has no shortage of them. As noted under ArtificialBrilliance. the Roaches in the game have a surprising amount of AI built into them, which is impressive given that even modern games usually give them pre-scripted animations or simply render them as particle effects.
* CreepyMonotone: The G-Man, the Black Mesa PA system, and the [=HECU=] marines' radio chatter. Funnily enough, the marines sound like normal human beings in ''Opposing Force'', where they're your allies.
* CurbStompCushion: By the second day of the incident, the HECU is being steadily overwhelmed by the aliens, but as far as the player sees they tend to win the individual skirmishes. This suggests that the aliens are only winning because of superior numbers (a whole army vs a single special forces battalion) and that the marines are giving as good as they get. It's true that they're still enemies of the player ([[FieryCoverup and everyone else in Black Mesa]]) but it's still easier to root for the humans during an alien invasion.
* CutAndPasteEnvironments: ''Opposing Force'' has a rather odd case of this. When using the Displacement weapon, you can teleport to a random location somewhere in the Half-Life universe, and these locations are different any time you load into a new story map. However, after discovering about the first 5 or 6 maps, you come to realize that the later maps will reuse the previous locations with a slight variation on the items in the area. Basically, once you've used the Displacement Gun a certain amount of times, you've basically seen all the locations.
* CuttingTheKnot: The player can beat "On A Rail" the intended way, unlocking paths forward for the rail car and using it to progress... or the player can just foot it for most of the chapter and SequenceBreak at several locations. The only places riding the tram are required is to destroy some concrete barriers, go up an elevator shaft, and pass through some electrified water.
* DamnYouMuscleMemory: "Jump" in the [=PS2=] port is L1 by default; luckily, the schematic is remappable.
* DaylightHorror: All but one of the outdoor scenes take place during the daytime. Most clearly demonstrated when Gordon has to dodge tentacles and headcrabs coming out of the sand.
* DeadCharacterWalking: The original has this: if an NPC has scripted dialogue, but you kill them before they begin to speak, the corpse will speak anyway. The mouth moves and the audio can be heard, but otherwise he is dead. (This works at least on the security guard at the end of the Power Up sequence.)
* DeusExNukina: [[spoiler:Happens to Black Mesa at the end of ''Opposing Force''.]].
* DevelopersForesight:
** In ''Blue Shift'' during the ''Captive Freight" level, you come across two scientists in your search for Dr. Rosenberg. If you actually try to backtrack with these two scientists following, you would come to realize that there is an invisible wall that will not allow the scientists to walk any further. That's because if you were able to backtrack far enough, you would come across the breakable wall that you would eventually learn about from Dr. Rosenberg that leads to where his colleagues are creating the portal device to escape Black Mesa. The reason for the invisible wall was so that you couldn't break the story and have two random scientists waiting at the elevator when Dr. Rosenberg leads you to it later on in the story.
** Also in ''Blue Shift,'' if the player destroys the wall hiding the elevator to the portal chamber ''before'' Dr. Rosenberg leads you back to it, you will soon realize that he will have a different line-of-dialogue regarding the fact that Calhoun has already found the hidden elevator instead of the normal dialogue to destroy the wall.
** The ammo belt feeding the M249 in ''Opposing Force'' is fully animated, being properly removed when reloading while there's still ammo and the belt actually running dry. This is as opposed to other games when the belt is infinitely long and mysteriously disappears when reloading. Most games, even modern ones, don't even do this.
** One part of ''Opposing Force'' has Shephard finally catching up to Freeman and seeing him just as he jumps into the Xen portal [[POVSequel (which the player does in the main game)]]. Should the player manage to kill Freeman in the very small time window he is visible, the game grants a NonStandardGameOver for breaking story canon:
POST MORTEM:''' ''Subject attempted to create a temporal paradox.''
** The player can also follow Freeman through the portal, resulting in them coming out in the same area as Gordon, albeit several feet away and over a bottomless pit. There's just enough time for the player to catch another glimpse of Freeman (and maybe take a shot at him) before falling and getting the same NonStandardGameOver as the previous example.
* [[DonutMessWithACop Donut Mess with a Security Guard]]: In ''Blue Shift'', the fat security guard in the firing range is seen trying to reach for his holstered gun while holding a donut with the closer hand. Later, a scientist tells another guard "Shouldn't you be off guarding some coffee and donuts?"
* DownerEnding: For ''[[spoiler: Half-Life]]'' and ''[[spoiler: Opposing Force]]'', [[spoiler:Gordon and Adrian are placed into stasis as some sort of mercenaries. It extends even farther - the Black Mesa incident attracted the [[BigBrotherIsWatching Combine]] to Earth, completely enslaving it, and Adrian's dialogue with G-Man implies he'll be frozen for a very, very long time.]]
* DumbJock: The graffiti the Marines leave on the walls to intimidate Gordon are full of misspellings.
* EarlyInstallmentWeirdness:
** The general design of the game and its Expansions are much brighter colored than its sequel.
** The Vortigaunts, due to the general lack of knowledge about Xen in this game, are called "Alien Slaves" [[AllThereInTheScript in the game files]], and talk in a stereotypically high-pitched, "alien" voice, as opposed to the monk-esque manner they do in the sequels.
** Ally and enemy alike can [[LudicrousGibs explode into a bunch of body parts]], which isn't as prominent in later installments.
** The Alpha version of the game was intended to be very different. The art style was more campy and unrealistic, with characters having very exaggerated features like bug eyes[[note]]this is where Barney first got his name, as it was a reference to the rather bug-eyed Don Knotts from Series/TheAndyGriffithShow[[/note]]. The level design was clearly more [[VideoGame/QuakeI Quake-esque]] involving a darker and more unrealistic color palette and guns that are held at the center of the player's view. Gordon's role in the story was apparently different, with all Black Mesa staff originally being against him. Gordon himself was a large, biker-looking man with a [[Main/BadassBeard huge beard]]. Dozens of enemies were cut from the game, some getting as far as to be modeled and scripted. Even the name was different, with the work-in-progress title of the project being ''Quiver'', a reference to the Arrowhead Project from Creator/StephenKing's Literature/TheMist.
* EarnYourHappyEnding: ''Blue Shift'' at least affords Barney a happy ending, though it's not easy.
* EarthIsABattlefield: In ''Opposing Force'', when a third party, Race X, becomes involved.
* EasterEgg: [[http://www.youtube.com/watch?v=OdLRZzCf_kk You can irritate VOX if you're particularly persistent]].
* EstablishingCharacterMoment: Many of the enemies (as well as the HECU) get one.
* EvilVsEvil:
** At multiple points you can encounter HECU marines battling Xen creatures, and wait around to take out the winner.
** Same goes for the encounters between the Black Ops and Race X aliens later in the Black Mesa incident.
* ExplosiveInstrumentation: Black Mesa's computers seem to be prone to this even ''before'' the resonance cascade.
* EyeBeam: Pit Worm in ''Opposing Force'' shoots one from its sole eye. Players that GoForTheEye can cause it to flinch, but won't otherwise harm it.
* FluffyTamer: ''Opposing Force'' has ''weaponized Barnacles''.
* FragileSpeedster: The female Black Ops Assassins have below average health, but are crazy fast, can make huge leaps, and on the highest difficulty setting, come equipped with a cloaking device. They're also {{Glass Cannon}}s, and can easily wipe half your health away in groups.
* FromBadToWorse: Dr. Freeman starts his day running late, gets trapped in the middle of an experiment GoneHorriblyWrong, has to escape from the ''creatures'' emerging from said experiment, ''then'' has to deal with the marines working on [[KillEmAll containment]], ''THEN'' black-ops ninjas. Even after that it gets ''even worse'' for him ''[[VideoGame/HalfLife2 and the rest of humanity]].''
* GettingCrapPastTheRadar:
** The Gonarch toward the end of the game was literally conceived because someone in the studio suggested "putting a huge testicle on a set of spider legs". Its name is also blatantly a portmanteau of "gonads" and "monarch".
** One of the cut monsters for the game was called "[[http://half-life.wikia.com/wiki/Mr._Friendly Mr. Friendly]]", a creature that would attempt to "rape the player to death" according to the behind-the-scenes book, ''Raising the Bar''.
* HilariousOuttakes: The [=PS2=] version had some DummiedOut voice lines like this, put to video [[https://www.youtube.com/watch?v=09pIWNW1o3w here]].
* GoForTheEye: In ''Opposing Force'', the Pit Worm can be briefly stunned this way, and the key to destroying the Gene Worm involves shooting its eyes repeatedly.
* GoneHorriblyWrong: The experiment that let the aliens in.
* GrapplingHookPistol: The detached barnacle in ''Opposing Force'', but only to biological matter. It also doubles as a lethal weapon, heavily damaging organic enemies (or in the case of headcrabs, reeling them in and instakilling them).
* HealThyself: The game follows the standard convention of instantly healing by picking up medkits. Unusually though, this actually appears to be canonical rather than a game mechanic. The syringes the scientist use to heal you (as well as the wall health kits in the [=PlayStation=] 2 port) have some weird green liquid in them that instantly heals all your wounds, and the medkits appear to contain the same substance. This may seem odd, but when you get to Xen, you encounter several pools of water that also magically heal you. The abundance of human corpses around Xen (as well as the location of an actual research outpost in ''Blue Shift'') suggests that the technology for this was stolen from the aliens via these pools.
* HyperspaceArsenal: By the end of the first game, Gordon is carrying [[WeaponOfChoice a crowbar]], [[StandardFPSGuns a 9mm handgun, a shotgun, a sub-machine gun]], [[RevolversAreJustBetter a revolver]], [[StuffBlowingUp grenades, an RPG, laser tripmines]], [[FrickinLaserBeams a laser gun]], [[DisintegratorRay a bigger laser gun]], [[BeeBeeGun an alien gun with living bullets]], [[StuffBlowingUp satchel charges]] and [[OrganicTechnology snarks]]. Plus ammunition. The worst example is the Gluon Gun, which is a ''backpack mounted nuclear reactor.''
* IJustWantToBeBadass: The first game was one of the first FPS games to avert this trope, and the game was remarkably atmospheric as a result. Ten years on, the atmosphere remains, but Gordon's [[TookALevelInBadass taken a level in wish-fulfillment]].
* IndecisiveDeconstruction: The first game can be read as a deconstruction of the TropeCodifier ''VideoGame/{{Doom}}''. The basic premise (an experiment into teleportation technology [[GoneHorriblyWrong goes horribly wrong]]) is basically the same as ''Doom''. Like ''Doom'', there is very little plot exposition. But unlike ''Doom'', ''Half-Life'' showed you exactly how terrifying this kind of scenario would be if it happened in the [[RealLife real world]]; you must think and ''not'' act like a stereotypical SpaceMarine in order to remain alive. And of course, this kind of experiment would require immense levels of government funding. Necessitating a large covert laboratory. And thus, when everything goes wrong the military have to be called in to ''keep'' things covert. However, the developers have at no point implied any critical intent. Thus, ''Half-Life'' is arguably an unintentional deconstruction. Also, given how influential the first game was on all future shooters, [[SeinfeldIsUnfunny the game seems like a played-straight example of the genre to someone raised on modern shooters]].
** It's also a reverse of ''Doom''. You're playing a guy who just started his job and doing his job - his first real work he's done just happens to mark the end of the world as he knows it. And right when he think he's out of the chaos the rescuing marines are there to kill him. The security guards, which in ''Doom'' are possessed and attempt to kill you, are friendly and are just trying to survive.
* InformedAbility: The most we ever see of Gordon Freeman actually being a ''physicist'' is when he pushes a cart into the anti-mass spectrometer. Barney lampshades this in the sequel.
* JustFollowingOrders: Pretty much the extent Gordon had to do with the resonance cascade.
** Then the marines who are called in to take out the scientists - then the black ops team who are called in to take out the ''marines''.
* LightningGun: The Shock Roach is a ''living'' version of this trope.
* LivingWeapon: The Spore Launcher, Shock Roach and Barnacle Grapple from ''Opposing Force''. The Hivehand from the original game may count as well.
* LooseCanon: ''Opposing Force'' and ''Blue Shift''.
* ManualLeaderAIParty: In ''Opposing Force'', you're usually teamed up with a squad of AI marines which you can direct, and use to perform certain functions (but you can't directly play as one of them).
* MilitariesAreUseless: While the marines are pretty tough, and individually competent, the guy who gave them orders is probably very, very dumb. The lab accident engineered an inter-dimensional alien invasion? Let's kill the security guards to prevent them from doing their job! A particular scientist seems pretty good at killing loads of aliens for us? Let's devote all our resources to taking him down! Now because of all this mess we have [[LeaveNoWitnesses plenty of witnesses to kill]]? Let's shoot them on sight instead of gathering them (and ''then'' shooting them)! And now our soldiers are being overwhelmed by the aliens that just keep coming? Let's send ''other'' soldiers to kill these soldiers! In the end, they evacuate and just nuke the complex to end the resonance cascade, leaving [[PlayerCharacter Freeman]] alone to go to the alien dimension and stop the invasion.
* MonsterCloset: The game explains it by way of the monsters getting into unused drywalled-off corridors due to random teleporting.
* NoIndoorVoice: The HECU Marines, due to their voices always sounding like they're coming out of walkie talkies. Even {{lampshaded}} by one line they say while idle: "[[WithCatlikeTread Squad, quiet down!]]" at the same not-very-quiet level.
* NoOSHACompliance: Apparently Black Mesa was built by people to ensure no employee survives in even the smallest emergency.
* NotSoStoic: The HEV suit computer is usually, well, mechanical, with no inflection on its words. But when Gordon is on the verge of death:
--> '''HEV Suit:''' ''(Urgent tone)'' [[PunctuatedForEmphasis EMERGENCY! USER! DEATH! IMMINENT!!]]
* NotSoDifferent: Invoked by the G-Man towards Adrian Shepard.
-->'''G-Man:''' I admit, I have a fascination with those who adopt and survive against all odds... they rather remind me of myself.
* PlanetLooters: Race X in ''Opposing Force''.
* PortalNetwork: Xen has one. Gordon uses it to navigate the place, as he often finds himself trapped inside small floating islands that can barley sustain a few animals (such as the first real island), or even "islands" that are just rocks that have just enough to stand on. ''Why'' they have one is a mystery however, as the aliens are repeatedly shown to be able to teleport wherever they want, even in groups, as a consequence of the Nihilanth's control.
* ThePrecariousLedge: During the "Surface Tension" section, you have to fight Marines along the side of a cliff face. It becomes extremely narrow in places and can be nerve-wracking for people with a fear of heights.
* PunchPackingPistol: For some reason, the same 9mm cartridges do more damage when fired from the Glock than when fired from the [=MP5=]. Also the Glock is given the miraculous ability to be fired underwater. The Python does far more damage than the .357 it's supposed to be as well, doing three times more damage than Opposing Force's M249, which fires rifle rounds that fairly realistically took down marines in full body armor after 3-5 hits.
** In reality a 9mm Glock can actually fire underwater, although the bullet would only travel a few metres and would do little damage.
* PuzzleBoss:
** The Tentacles when you first encounter them in the main game, and the Pit Worm in ''Opposing Force''. Both are defeated similarly, by activating the surrounding machinery, which also in both cases requires the player to sneak or run past the boss several times to reach the necessary switches.
** The Gargantuas. Each one you encounter has some method to kill it using the environment. Technically, you can kill one with your weapons, but having maxed out ammunition for every weapon in your inventory is just ''barely'' enough firepower.
* SecondaryFire: Several weapons featured this. Mostly they were simple things like a laser sight or a scope, but in some cases it basically made the weapon two guns in one, and in other FPS games of the time it would've been a separate weapon altogether rather than a secondary fire. It can be said that Half-Life 1 actually had 19 weapons instead of 15.
** The SMG/assault rifle had an M203 grenade launcher mounted under that could hold ''ten grenades'' and never needed to be reloaded. This, combined with its reasonably common ammo, made it somewhat overpowered.
** The shotgun could [[GunsDoNotWorkThatWay fire both barrels at the same time (even though it only has one barrel)]], giving you twice the damage at the cost of accuracy, ammo, and pump time. Very similar to the Super Shotgun weapon in {{VideoGame/Doom}} II.
** The Tau Cannon's secondary fire was a powerful, charged, pixel-accurate laser beam that changed it from a rapid-fire infantry muncher to a single shot anti-vehicle weapon.
** The Hivehand had two modes of fire: the primary fire launched heat-seeking "thornets" at a semi-automatic rate. The secondary function "dumb fired" all the thornets in quick succession; much faster than the primary fire, but without the homing ability.
* ScenicTourLevel: The former TropeNamer. Gordon takes a tram in the original, Shepard takes a chopper ride with his squadron in ''Opposing Force'', and Barney makes his way to an elevator while passing through security.
* SequenceBreaking: In "Blast Pit," it's possible to save the scientist who would have been taken away by a Tentacle by quickly rushing over to him, and speaking to him; cancelling the scientist's scripted event.
* SharkTunnel: "Crush Depth" in ''Opposing Force'', where a few of the lovely icythyosaurs have broken out of.
* {{Sidekick}}: Barney the recurring security guard.
* SlaveMooks: The Vortigaunts.
* SplitScreen: ''Decay'''s method of display.
* StarfishAliens: Most of the aliens barely resemble any form of Earth wildlife.
* StopPokingMe: Walking into certain locked doors repeatedly in the first game will [[http://www.youtube.com/watch?v=OdLRZzCf_kk start to drive VOX crazy.]]
** The Same Vox can be poked fun in the PC Mod of ''Decay'' 's Hazardous course chapter.
* TeamworkPuzzleGame: ''Decay''.
* TemptingFate: You can overhear one HECU trooper telling another that he killed a bunch of scientists and "not one of them fought back", and proceed to do exactly that.
* TenSecondFlashlight: Severely {{downplayed|Trope}}. While the torch does recharge faster than its juice is spent, it lasts for a really long time. Most of the time, you won't see the icon grow dim past the beam portion of it.
* TitleDrop: "Blue Shift" is the InUniverse name of the security shift that Barney works on.
* TrackingDevice: Apparently Freeman's HEV suit has one, and both the science team and the military have been using it to monitor his location and, in the latter's case, set up ambushes.
* TwoKeyedLock: The test chamber has to be unlocked by two scientists each activating retinal scanners.
* UnbrokenFirstPersonPerspective: The TropeCodifier for the use of this trope in a narrative context. As described above, the game unfolds entirely from the perspective of Gordon Freeman, with no cutscenes.
* {{Unwinnable}}: Unlike its sequel, you won't get a NonStandardGameOver if an essential [=NPC=] gets killed.
* VaderBreath: The "Gonomes", the final evolution of the Headcrab Zombies, could easily be identified by a rattling noise.
* VengefulVendingMachine: Early in ''Opposing Force'', Shepard encounters a fat security guard named Otis with his hand stuck in a vending machine. The guard curses, going like "Stupid machines!" and asks the player for a quarter. It's possible to operate the machine with the Use key, and this makes a candy bar pop out. However, the guard does nothing if you do.
* VideoGameCrueltyPotential: With the exception of a few [=NPCs=] necessary to advance, nothing is stopping you from killing every scientist or guard you see as long as you have a weapon. Killing said [=NPCs=] results in a NonStandardGameOver.
* VisualPun: In ''Opposing Force'', to defeat the [[PuzzleBoss Pit Worm]], you have to first reactivate a Gear Box, and open a pressure Valve. [[DontExplainTheJoke Hmm...]]
** For a bonus, before activating the valve you have to use a Steam Vent. Since ''Opposing Force'' came out years before Steam, it's coincidental, but still pretty funny.
* WeaponizedOffspring: The Gonarch creates Headcrabs (who are essentially smaller versions of it) during the fight against it.
** According to WordOfGod, the Spore Launcher from ''Opposing Force'' is an infant Shock Trooper.
* WhatHappenedToTheMouse: Race X and poor Adrian Shephard. Marc Laidlaw has said that he doesn't want to develop further on Race X, saying that they were only experiments by Gearbox for future games, and that Gearbox would have developed them further if they were still doing expansions for Half-Life. He has also jokingly called Adrian a case of Schrödinger's cat, as he is in a state of being both canonical and non-canonical at the same time. His ultimate fate depends on what Valve want to do with him in the future. Gabe Newell has reportedly been wanting to incorporate him in the canon for some time.
* WhatMeasureIsAMook: both {{Mook}} and OneManArmy are {{Deconstruct|ion}}ed; sneaky players can listen in on the {{Arm|iesAreEvil}}y as they have weird self-hating conversations about [[CavalryBetrayal slaughtering hundreds of scientists who expected them to RESCUE them]] - and later their rage at the player, who they believe was the mastermind behind the invasion and have been slaughtering their comrades wholesale. On the other hand, one of the Marines laments having none of the scientists fight back.
** You play as a HECU marine in the ''Opposing Force'' expansion pack. While said Marine is comatose for most of the original game and wakes up just as the military begins pulling out, your allies are all trying to work together to pull out.
* WhyDontYaJustShootHim: Double Subverted. Two marines who capture Freeman decide they should kill him instead of taking him in for questioning, in case he escapes and causes more trouble. But they ''don't'' shoot him; They just leave him in a trash compactor, still breathing.