Forget Gordon Freeman for a second. While the nerd in the HEV suit was busy jumping over toxic sludge, Corporal Adrian Shephard was falling out of an Osprey. That’s where the half life opposing force walkthrough actually begins—not in a tram, but in a crash.
Most people remember Opposing Force as just an expansion pack. It’s way more than that. Gearbox Software, led by Randy Pitchford back in 1999, basically rewrote the rules of what an expansion could be. You aren't the hero saving the day. You’re the guy sent in to clean up the mess, which usually means "silencing" the witnesses. But then the aliens show up. Then the black-ops assassins show up. Suddenly, your mission parameters don't matter because you’re just trying not to get eaten by a Pit Worm.
The Early Chaos and Waking Up
You wake up in a medbay. Everything is broken. If you've played the original game, seeing the Black Mesa disaster from the eyes of a grunt feels weirdly personal. The first thing you need to realize in any half life opposing force walkthrough is that your wrench is your best friend. Seriously. Don't waste your bullets on the small stuff.
The opening chapters—"Welcome to Black Mesa" and "Missing in Action"—are slower than you’d expect. You’re navigating cramped vents and shattered hallways. You see the aftermath of Freeman’s chaos. You see scientists who are terrified of you. It’s a tonal shift that still feels gritty even decades later. Pro tip: when you find the fat guard (Otis), keep him alive. He’s got better aim than the regular security guards and his Desert Eagle packs a massive punch against Headcrabs.
Why the Combat Feels Different
Unlike Gordon, Shephard is a trained soldier. You get access to the PCV (Powered Combat Vest), which functions like the HEV suit but feels more "military." You also get a bunch of toys Gordon never touched. The sniper rifle is a game-changer. In the original Half-Life, long-range combat was a bit of a mess. Here? You can actually pick off targets from across a hanger.
Then there’s the Barnacle. Yes, you can literally pick up a Barnacle and use its tongue as a grappling hook. It’s gross. It’s fleshy. It’s also the only way to get through some of the vertical platforming sections later in the game. If you aren't using the Barnacle to bypass annoying radioactive pits, you're making the game twice as hard as it needs to be.
Navigating the Race X Nightmare
Halfway through the game, things get weird. The "Race X" aliens show up, and they aren't the ones Gordon was fighting. These guys are meaner. The Shock Troopers are the worst. They’re these blue, multi-armed nightmares that throw spore grenades and drop "Shock Roaches" when they die.
If you're stuck on a half life opposing force walkthrough section involving Shock Troopers, remember: they have a rhythm. They fire, they pause, they fire. Use the M249 SAW to suppress them. This is the big machine gun that Gordon never got, and it chews through ammo like crazy, but it’s the only thing that stops a Shock Trooper in its tracks.
"The inclusion of Race X was a bold move by Gearbox because it meant they didn't have to just rely on the existing Xen lore. It made the world feel bigger and more chaotic." — Marc Laidlaw, former Valve writer (paraphrased from various development retrospectives).
Pit Worm’s Labyrinth
The Pit Worm is the "boss" that everyone hates because it feels like a puzzle more than a fight. You’re in a waste processing area. You can’t just shoot the thing. You have to activate two different valves—Steam and Pressure—and then hit a button to flush the chemicals.
It’s tedious. You’ll die a lot because the worm has a beam attack that tracks your movement. The trick is to stay behind the metal pillars. Don't even try to shoot it with your shotgun; it’s a waste of shells. Just focus on the levers. Once you hit the final switch, the worm melts, and you can finally move on to the endgame.
The Discrepancy of the Black Ops
The most difficult enemies in Opposing Force aren't the aliens. They’re the Black Ops. These are the guys sent in to kill the soldiers who failed to kill the scientists. It’s a messy "clean up the cleaners" situation.
These guys are fast. The female assassins are back, and they’re even more annoying in the dark. Use your Night Vision Goggles (NVGs). Most players forget they have them. While Gordon had a flashlight that ran out of batteries in five seconds, Shephard has green-tinted NVGs that actually let you see the assassins' silhouettes through the fog.
The Displaced Chapter and Teleportation
The chapter "We Are Not Alone" is a trip. You literally arrive at the teleportation chamber just as Gordon Freeman is jumping into Xen. You see him. You can actually jump into the portal after him, but it’ll result in a "mission failure" because you've caused a temporal paradox.
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Instead, you have to use the Displaced weapon. This thing is a portable teleporter. It’s one of the coolest, most underutilized mechanics in the game. It uses "Xen crystals" as ammo. Primary fire shoots a big ball of energy. Secondary fire teleports you to a "safety" zone in Xen where you can find health and ammo before popping back into Black Mesa. It’s basically a cheat code built into the lore.
Handling the Gene Worm Final Boss
The end of the half life opposing force walkthrough happens deep underground. You’re not fighting the Nihilanth. You’re fighting the Gene Worm. It’s this massive, green, fleshy pillar of a monster that’s trying to bridge the gap between worlds.
Here is the secret to winning:
The Gene Worm has two "eyes" (or sensory organs) on the sides. You have to shoot both of them with the mounted laser cannons until they shut. Once the eyes are closed, its stomach opens up. That’s the only time it’s vulnerable.
Most people try to use the RPG or the SAW here. Honestly? Don't. Use the mounted guns. They have infinite ammo and they’re designed for this specific fight. If you try to use your handheld weapons, you'll run out of ammo before the worm is even at half health.
After you deal enough damage, the whole place starts to blow. The G-Man appears, puts you on a tram (sound familiar?), and "detains" you. Shephard is still technically "waiting for further orders" in the Valve lore, which is a nice way of saying they put him in a box and haven't used him since 1999.
Essential Tips for Surviving Black Mesa
- The Spore Launcher is a sniper rifle. Use the organic launcher you get from the aliens. The spores have a slight arc, but they deal massive splash damage. If you're low on traditional ammo, this thing is a lifesaver.
- Squad management matters. You can find Engineers to blow open doors and Medics to heal you. Don't let them die. If you see a Medic, stand in front of him and press your "use" key. He’ll top off your health for free.
- The Pipe Wrench has a secondary attack. Hold down the right-click. Shephard will wind up for a massive swing. It can one-shot a Zombie or a Bullsquid if you time it right. It’s much more effective than the crowbar ever was.
- Save your 357 ammo. The magnum is rare in this expansion. Save it for the Black Ops snipers. You’ll need the accuracy and the stopping power when you're pinned down in the parking garage levels.
The beauty of Opposing Force is how it fills the gaps. You see the G-Man arming the nuclear bomb that Gordon thought he escaped. You see the military’s total collapse. You realize that while Gordon was the "One Free Man," Shephard was just another pawn in a much bigger game.
To get the most out of your playthrough, stop rushing. Look at the scripted events happening in the background. Gearbox put a lot of effort into showing the HECU soldiers getting slaughtered by the very things they were sent to contain. It’s a grim, claustrophobic experience that holds up surprisingly well, even by 2026 standards.
Check your corners, keep your Medic alive, and for the love of everything, don't fall into the trash compactor.
Next Steps for Players:
- Verify your version: Ensure you are playing the Steam version with the "High Definition" pack disabled if you want the original, grittier 1999 aesthetic.
- Master the Displacer: Practice the secondary fire teleportation in the "The Package" chapter to find hidden ammo caches that are otherwise inaccessible.
- Key Bindings: Rebind your "Night Vision" key to something reachable like 'F' or 'G'. You will need to toggle it rapidly during the Black Ops encounters.