The entire course of the game is one for the Player Character. Gordon Freeman went from a hapless, likely terrified scientist with a crowbar desperately struggling to survive the catastrophic aftermath of a science experiment gone wrong to a One-Man Army armed with exotic physics weapons who venture into a hostile parallel universe as possibly Humanity's last, best hope against an Alien Invasion without hesitation, having despite the overwhelming odds against him ran, thought, shot, and lived through every obstacle and every opponent alien, Human or otherwise which got in his way.
The booting up of the HEV suit. Even without the Klaxon Beat, the music — along with the list of executed programs and suit functions being turned on — sends chills up your spine. The HUD slowly flickering on, the chromatic aberration along with the health and armour values, and the hands extending in front of the camera in awe of the suit is a testament to how powerful one feels in the Mark IV HEV suit.
Early on in the chapter Unforeseen Consequences a scientist kills a headcrab with a computer monitor. YMMV of course, but you have to give the old guy some credit for showing some real spunk to the eldritch invaders.
One moment in On A Rail for a lonesome security guard who could accompany Freeman: when Freeman and the guard reached the rocket carrying a satellite that needs to be launched for the Lambda Team to have a chance to reverse the resonance cascade (which was aborted by the military), that guard tells Freeman to go ahead with prepping the rocket silo for the launch while he holds the fort upstairs. Halfway down, HECU soldiers bust into the area. Said security guard proceeded todefiantly holdthe ground against an entire squad of ruthless, body-armour wearing, submachine gun wielding HECU with nothing but a security guard jacket and his pump-action shotgun. Freeman only gets to hear the battle taking place off-screen, but when he comes back up, Freeman finds the security guard did more than just hold them off: he managed to kill off the entire HECU squad all by himself. Too bad he took a fatal wound and bled out soon after, but he still bought Freeman enough time to do what needed to be done, even at the cost of his own life.
Security Guard: [Bleeding out] You should see... [Coughs] You should see the other guy... [Dies]
The Lobby Ambush in Questionable Ethics. A quick but vicious fight against the toughest enemies of the game, in which the player is given suitable kudos for surviving by the NPCs as well as firmly establishing Gordon Freeman's role as a One-Man Army at that very point to them.
Scientist:[seeing the carnage] Look what you did...! Security Guard: (awestruck) Holy shit... Scientist: I... can't believe what you did!
Ensure that the guard you meet upon leaving the Tripmine warehouse is alive during Surface Tension: After another guard realizes you aren't Marines, we get this exchange:
Guard:Jackson? Good God, man, how many lives do you have?! Jackson: Heh, none, if it wasn't for my new buddy here.
And although you can still access the guard's mini-armory even without Jackson accompanying you, it counts doubly as Heartwarming if you manage to bring back Jackson to his fellow security guard buddy.
Magnum ammo is a little more plentiful in this game. As such, you'll be using it more often... and every time you kill a hostile Headcrab Zombie or HECU marine with it—hell, just firing that hand cannon, thanks to the updated graphics and sound—will make the player feel powerful, especially since you can go into its optional iron-sights mode by holding the right-mouse button for much more precision to prevent wasting precious Magnum ammo.
Related to that, the satisfaction of plugging one of those Black Ops Assassins with it and getting the Dead Reckoning achievement is just amazing.
The absolute feeling of sheer euphoria one may feel after they manage to damage the deadly Apache Gunship that is sent after them once Freeman reaches the Dam on the surface enough via the TauCannon, with the Apache fleeing in a cowardly fashion once Freeman manages to significantly damage it to the point where it's both a near-destroyed smoking and flaming wreck never gets old...!
Headcrab zombies. Yes, you read that right. If you don't kill them with a headshot, the headcrab will leap off the corpse it was controlling, making you waste extra rounds to kill it for good.
Doubly so for the ZEV, an all-new Zombie variant encountered in Xen. That high-impact, reactive power armour it's wearing isn't just for show, either; it'll ignore a good portion of all incoming damage, making it practically mandatory to use headshots or explosives to put it down for good.
The Gargantuas are much more powerful this time around—you won't be able to just kill these beasts with a massive stockpile of ammo. You have to use the environmental hazards present to kill them when they show up, and pray you can outrun them long enough to get to said hazards.
Speaking of, one segment of Interloper drops you right into a Gargantua nest, and a Chase Scene ensues where you have to outrun dozens of them. On finally making a long jump across a pit they cannot cross, you're in the clear, and you look back to see all of them on the cliffs you've just left, roaring and flaming the air.
The Tentacles you fight in the Blast Pit are a lot more sensitive to noise and movement.
Not only that but the moment you activate the rocket engine has been amplified in intensity thanks to epic guitar music that plays as you ascend back to press the button, giving way to even more urgency and a greater feeling of badassery than before. It's timed so that if you throw caution to the wind and just run to the button as fast as you can, the guitar will fade to piano around the same time as the boss is dying.
The Vortigaunts get a subtle one in the form of their electric bolts—they're much more accurate and quick to charge; if you don't keep moving or put them down fast, you'll get a nasty jolt.
The Ichthyosaurs—they tend to lurk in murky water, so you won't see them until they're practically on top of you. Here's hoping you've got a steady trigger finger and nerves of steel...
On the human side of things, the Apache gunships used by the HECU pack a hard punch and can take punishment just as well as they dish it out. Bring your heaviest firepower, and find cover, you're gonna need every bit of both.
A villainous example. When Freeman is navigating the thin paths along the cliffs, there's a moment where, upon exiting the tunnel to said cliff exterior, you can catch a quick glimpse of a trio of HECU bombers making a fly-by near your airspace. Later you can witness a duo of them make a bombing run to a Black Mesa facility shown in the distance. As if that wasn't enough, the remains leftover from said bombing run are even shown in flaming, smoking ruins as well as the shockwave itself being visibly shown. Quite the attention to detail.
The HECU grunts get this, too. They have all their original strategic maneuvers, plus they can run and shoot, now. Oh, and they're more accurate with their guns. They even have medics!
Even the allies get some. While they still aren't as strong as the opposing forces, they're smarter.
Security guards will sneak up on enemies and put up a definite fight, lasting much longer most of the time than they normally did. They also use a wider variety of weapons, ones that pack a punch, such as the revolver and shotgun.
Scientists will use caution and tend to stay out of your way more often so they don't inadvertently die as easily, and they still heal, much better actually.
Hell, even the Alien Crafts (commonly referred to as Manta Rays or just simply Mantas by fans) are more badass than they were in the original, even though they're still simply background objects. They don't make the same jittery movements and animations as they did in 1 due to the much more powerful engine, and the dogfights they have in ''Forget About Freeman'' are stunning.
As of the Surface Tension: Uncut Update, there's a scene where one chases a military jet fighter (contrary to a previous scene where one was chased by a jet fighter itself) and another where it uses its belly cannon and vaporizes a tank that was in the way.
"This is Mastiff-1. Multiple targets in the open. 3 o'clock! 50 metres, on the way!" (tank proceeds to provide covering fire to the soldiers, when suddenly...) "Enemy air incoming! Shit, shit, shit!" "Son of a... Back up! Back up! BACK THE FU—" (tank is hit by the Manta's laser and explodes)
And as of the 1.0 beta, they take out a pair of HECU LAVs in the surface battle in Forget About Freeman
The Alien Controllers have to take the title for the crown. They fire faster, move more unpredictably, and can toss explosive barrels your way a la the Gravity Gun.
Over the Xen chapters, Gordon Freeman would occasionally run into pods suddenly appearing in bouts of trans-universal teleportation, carrying vital supplies of ammo, batteries and health packs. As it turns out, the Lambda team and complex survived the attack by Xen forces from the last Black Mesa level, and they are sending Gordon all the help they can to give him the best possible chances of surviving the hostile realm and stopping the Alien Invasion at its source. They even managed to send encouraging notes to lift his spirits in some of the cache, and drinks and beverages for the poor Vortigaunts oppressed by Nihilanth you ran into!
Note 1: "Nothing in life is to be feared, it is only to be understood" - Marie Curie
Note 2: Press on, Freeman!
You can't help but feel this way when you get to Gonarch's Lair. The whole chapter has been completely overhauled (compared to the original), and the fight/hunt/showdown against the Mother of Headcrabs (which lasts the WHOLE chapter) will leave you very, very satisfied. Don't believe us? See for yourself. This is the original Half-Life's version; here's Black Mesa's version (protip: begin by comparing the length of each video).
During Interloper, as the player goes further into the Alien Grunt factory, they'll have to face off against dozens of Alien Grunts and Alien Controllers while having to handle increasingly scarce ammunition reserves. But at the midway point, you'll find these strange green crystals. What do they do? Provide you with unlimited depleted Uranium-235, allowing you to use the Gluon Gun and Tau Cannon as much as you want. It is incredibly satisfying to watch the Grunts and Controllers get utterly decimated in the ensuing battles.
The Nihilanth in the original game was a rather underwhelming boss fight: his most dangerous attack was teleporting you to other arenas and letting his slaves deal with you. By the end of the fight, he's reduced to throwing occasional weak energy blasts. In Black Mesa? He's portrayed as every bit as powerful as the lore makes him out to be, telekinetically throwing phone booths, cars, and even tanks through portals at you, covering the area in giant psychic lasers, energy shields, and deforming the landscape around you with earthquakes. When he finally goes all-out in the final phase, it's downright scary to see the sheer amount of energy he's channelling... and all this makes what canonically happened in the aftermath of the Nihilanth's death (giant portal storms teleporting millions of Xen creatures all over Earth) much more understandable.
Nihilanth: Now die! NOW DIE! NOW...!
It gets even better when you consider that he was likely still holding the way closed for the Combine; if he'd been able to bring every ounce of his power to bear against Gordon, there's no telling how he would have fared.
Getting the Late For Work Achievement, beating the Nihilanth in just under 4 minutes, it's a tough job but if you pull it off, Gordon was more than prepared.
. Even without the Klaxon Beat, the music — along with the list of executed programs and suit functions being turned on — sends chills up your spine. The HUD slowly flickering on, the chromatic aberration along with the health and armour values, and the hands extending in front of the camera in awe of the suit is a testament to how powerful one feels in the Mark IV HEV suit.