Omri mentioned a mod called gmDoom last month, which allows you to bring the Doom experience, including weapons, enemies, HUD, and entities, into Garry's Mod. After watching a few weeks pass as bugs were squashed and updates were released, I decided it was finally time to pull-start this particular chainsaw and take it for a spin. I also decided, instead of just playing around, to really play. Specifically, I wanted to play through the entirety of the Half-Life 2 campaign, using only the gmDoom HUD and weapons. Space Marine, welcome to City 17!
Hm? What? Who? Space Marine is skeptical.
After getting off the train in City 17, I realize how happy I am to be an angry, violent Space Marine instead of a befuddled, bespectacled scientist. Gordon Freeman didn't pick up a weapon until a good half-hour into Half-Life 2, but Doomguy is always packing a pistol, a chainsaw, and his fists. Rather than wandering through the beginning of the game, helplessly watching as citizens are abused at the hands of the Metrocops, I can immediately right some wrongs by applying a healthy dose of SPACE VIOLENCE.
So, when I see a Metrocop shove a citizen, I punch him to death (the Metrocop, to be clear). That annoying flying camera robot gets a taste from my pistol. What's this? Other cops, standing around doing nothing violent? Not on my watch! They die. I approach a couple citizens as well, just to see if weapons work on them too. (Weapons work on them too.) Oh, and that cop who tries to make me pick up a soda can and put it in the garbage? I saved the chainsaw for him.
Marines. Always. Recycle.
Before long, I'm in the canals, fighting enemies who can actually fight back. It mostly works well: the weapons are effective and feel natural after a few minutes of play, though you have to be pretty darn precise with your aim for long-distance kills. It's also a genuinely neat experience: the sights and sounds of the throwback Doom weapons mixed with the atmosphere and enemies of Half-Life 2. It's double-nostalgic. It's like combining two tastes I love, bacon and chocolate, into one violent, historic mouthful of video game.
Something else I notice: while it feels a little odd in this day and age to play a game where you're constantly staring at your own face, it does make your health quite a priority. Instead of a percentage or a colored bar, you get to look at your sad mug streaked with blood, a pretty visceral reminder that it's not your health meter taking damage: it's your own face. Finding medkits feels a lot more urgent when you're hurt so bad your hair is bleeding.
Space Marine needs food, badly.
Ammo for my Doom weapons, naturally, is not stocked in City 17, so I just spawn some for myself from the Garry's Mod menu when I run out. I try to also give myself new weapons when it feels appropriate. When Metrocops start using machine guns, for example, I give myself Doom's chaingun. When I remember that you don't get a shotgun until you get to Ravenholm, I give myself one anyway, because screw that.
After escaping City 17, I wind up deciding to skip the second half of the canal levels. Making a Space Marine drive a crummy boat powered by a fan just seems insulting. It's like making Willy Wonka eat a celery stick. He knows not of, and cares not for, such primitive tools. Fast-forward, then, to Ravenholm!
Plus a quick stop in Black Mesa East to kill a disgusting alien. You're welcome, Vance family!
In the zombie-patrolled streets of Ravenholm, our Space Marine seems quite comfy. Hideous shambling monsters, blood, gore, horror: these are what Doomguy was made for. I admit, I do pine for the Gravity Gun, because flinging giant circular blades into zombies is still awesome. The super shotgun works just fine, though.
These zombies don't shoot back? You got off easy this time, Earth.
After blasting my way through Ravenholm with kindred spirit Father Gregori, I decide to skip the driving sections of HL2 as well, mostly because the driving feels like 100% Half-Life 2 and 0% Doom, and the mix is what's really making this fun. I skip to the lighthouse at the end of the coastal maps, and dig in with the resistance as they fight off the Combine attack.
After defeating a few waves of drop-ship soldiers, I run into a little problem when the Synth Gunship arrives. I've given myself Doom 2's rocket launcher, but it only fires in a straight line, as opposed to HL2's laser-guided launcher. The Gunship doesn't shoot my rockets down, but there's no need: I keep missing because the Gunship keeps moving. Try as I might, I just can't hit the sucker. He, however, has no problem hitting me. It's time to call in reinforcements.
No shame in a Marine calling for backup. SPACE backup.
I use G-Mod to spawn a Doom Cyberdemon-- shut up, that is TOTALLY FAIR-- and the gunship and the Cyberdemon immediately decide they hate each other. (Isn't introducing one enemy to another enemy always awkward, like when your work friends meet your personal friends?) Unfortunately, the Cyberdemon is also unable to hit the gunship. Finally, exasperated, I just take out my G-Mod physics tool and hold the stupid gunship in place, letting the demon blast it to pieces. ALSO FAIR.
Hold still. This will only hurt a lot.
And, having used a physics tool from 2006 to help a cyborg demon from 1993 kill a biosynthetic airship from 2004... that's where my play-through of Half-Life2 abruptly comes to an end. It was a fun experiment, sure, but holding a three-dimensional gunship in the sky with my finger so a two-dimensional demon can whomp on it serves as a massive reminder: I don't just have two great games to play with here, I've got three, and I've all but forgotten about the Garry's Mod part of the experience. I've been eating bacon and chocolate, YES, but I've been completely neglecting the GLORIOUS BOTTLE OF BOURBON sitting right there to wash it all down with.
Time to switch from playing Half-Doom 2 and start playing a game I call Make Everything Fight Everything Else By The Lighthouse For Six Straight Hours!
Combine vs. Heavy Weapon Dudes!
The Combine win!
Pinky vs. Combine!
Arch-vile vs. Antlion Guard!
Antlion Guard wins -- but Arch-vile really does raise the dead Doom monsters! Awesome.
Antlion Guard vs. Spiderdemon!
Spiderdemon wins (eventually)!
Helicopter vs. Pain Elementals and Lost Souls!
Draw. Spawned helicopter doesn't seem to ever die, and Pain Elementals never seem run out of Lost Souls.
After making Everything fight Everything Else for six hours, I do, eventually, return to Half-Life 2 proper, mainly to see if I can take down a Strider with a Doom 2 rocket launcher (I can, and quite handily) and to try out the plasma cannon on the Combine (it works amazingly well). And, of course, to unleash the BFG on a store-front full of Combine soldiers.
Looks like the store... *sunglasses* ...is CLOSED.
Putting this mod into that other mod and putting both mods into Half-Life 2 is amazing. Do it! Do it now!
Installation: Mostly simple! However, you'll need a WAD file from one of the Doom games to import all the assets. If you don't own a Doom game, you can use a WAD file from the free shareware version of Doom and still get most of the weapons (I used Doom2.wad; full list of what the various WAD files give you access to here). Drop the WAD in the garrysmod/garrysmod folder in your Steam directory. Then, just subscribe to the mod on Steam Workshop and when you boot up Garry's Mod, it will be enabled. You can spawn all your weapons and monsters from the menu by pressing Q, and enable the HUD using the console code doom_cl_hud 1.
Also, and perhaps this is obvious, but you'll need Half-Life 2 installed for all the Half-Life 2 stuff.