What amazes me about Half Life 2 fanboys is that they bash Doom 3 nonstop yet they act like Half Life 2 was some sort of fucking gaming revolution.
But here's Doom 3 vs. Half Life 2, step-by-step:
Graphics: Doom 3, easily - HL 2 was on par with RTCW, and except for some nice facial animations, wasn't anything extraordinary. D3 had great textures, shading, lightning, and much better artwork.
Sound: Tie, both were good, though I felt Trent Reznor's sounds were a lot better than Id's sounds. Half Life 2 had some uneven volume levels as well.
Story: Doom 3, yes, believe it or not Doom 3 told its story better. It was a simple story, but it made sense (from a gaming standpoint) and flowed nicely. Half Life 2 was all over the fucking place and left too many unanswered questions.
Gameplay: Doom 3, because it actually felt like a Doom game, with its trademark tongue-in-cheek, comic book depiction of Hell and great bosses. Half Life 2 didn't even feel like Half Life, instead it played like a Greatest Hits of first person shooters. Here's the intro level, here's the driving level (that allows no freedom to drive wherever), here's the level where you defend yourself against hordes of enemies, here's the creepy town level...ugh. Real original. Doom 3 wasn't original either, but it did its job better. Where were all those enemies that we loved in Half Life? Instead what we get are a bunch of flying buzzsaw Phantasm rip-offs and lame "ant lions." Oh, and level transitions in HL 2 suck ass...you're crawling through city streets one level, then all of the sudden it seems like you're on a different planet with an airboat, running from different enemies. There was absolutely no coherence in the game design.
Replayability: Well both are extremely linear, but HL2 is WAY too scripted, so its about as exciting as gardening.
Multiplayer: HL2 wins, if only for the gravity gun and CS:S.
Doom 3 is the Slayer of modern first person shooters; it does only one thing, but it does it well and it's unforgiving and uncompromising in its approach. Half Life 2, meanwhile, is the Linkin Park of modern first person shooters. It gives the masses the tried-and-true gameplay features, and it relies on its immature idiot fanbase to sustain it. But then again, the Half Life series always were the diet coke of gaming.
Don't like carrying a flashlight? Get the flashlight/gun mod, or accept it as part of the gameplay. Hate spawning enemies? Did you even play the first two Dooms, moron? Not revolutionary enough? It's a Doom sequel, it never promised to be revolutionary, unlike the pile of shit that is Half Life 2. Just stop acting like a bunch of whiny bitches...though that is what Half Life fans are known for. You guys make Halo 2 fans look composed and dignified.
Of course, now all the little HL2 fanboys/Doom 3-haters are going to pick apart my post with their "OMG u liek teh doom 3 j00 are so gaaay dom3 is teh suxx0r lol !!11"