For those worried about spoilers... don't.
I've just soaked up my first 2 hours of Doom 3, and it was everything that I was expecting. I remember playing Doom 2 in my early highschool years, sitting and shaking at the edge of my seat. Granted these days, those 2D pixilated images in a 3D world aren't much to fright about, but back then, it gave me nightmares. This is even more of the same with a gorgeous facelift powered by 10 years of graphics, physics, and sound innovation. (I'm still shaking)
However, before you go buy this game, you should be aware of what it is, and most importantly, what it isn't. If you're looking for a game that has a storyline, characters, and dialog with any meaning, go ahead and turn around. Doom 3 plays much like a very dark Half Life without the puzzles (and I mean dark). The spaces are tight and cramped, the world is as interactive as it was in the original installments, and the game offers only a singular (and very linear) path from objective to objective.
Doom 3 is a shoot to survive game. The cinematics flow into and out of the game with beauty and the scripted events play on many of everyone's childhood nightmares. The lights are low and go out suddenly. Sometimes the only usable light you have is the muzzle flash from your weapon. Monsters come at you from shadows and attacking from all directions. The world is filled with moving machinery that confuses the eye with ominous shadows cast on bloodstained walls. You hear other people fighting and screaming behind locked doors. You hear monsters scratching thier way through corridors around and above you. Any student of the horror genre would recognize the time honored tools of fright that have been utilized with the flair of the best Hollywood producers.
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As scary as Doom 3 is, it doesn't play all that well. I'd hate to think that my Radeon 9600 XT is behind the times, but honestly, it can only handle this game at 800x600 resolution with medium detail. I shudder to imagine the graphics card that can play this game at 1600x1200 at the ultra-detailed setting. The load times are also a little much for my P4 2.4 GHz processor. The intensity is nearly lost in the 2-3 minutes I sit there and watch the load bar going nowhere. I also find the difficultly scales well over my head. With this kind of game, I can usually play at the medium setting and beat the game. However, on medium, some of the monsters that I would expect to go down in one or two shotgun shells take 3 or 4 blasts to the head before they fall. I know I'm not that great, but when you can't even see the target that well, how are you supposed to pull off headshots? Which brings up another question, why must I chose between using my weapon or the flashlight? The game doesn't allot you enough time to swap between the two effectively so there are times where you're either shooting blind or clearly seeing the monster ripping you to shreds.
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Overall, I give this game a C+. To really enjoy this game, you'll need a dream PC with a top of the line 256mb graphics card and full surround speakers. If you're looking for something to keep you up at night, Doom 3 is exactly what the doctor ordered. If you're looking for a game that people will still be playing a year from now, you'll have to look somewhere else.