Having just finished the game, let me share some thoughts.
First of all, I know that some people consider Doom 3 to be pretty much shit. I don't know why. Is it because it doesn't add anything particularly new to the genre? Doom 3 has premiered in 2004 and there are still games made who share that characteristic. Hell, when I reviewed Quake 4 a year ago or so, I said the exact same thing. So neither game is anything new. Is that a problem? I say it's not if the game's still fun. And Doom 3 is fun.
It's major asset is the atmosphere. The game's quite gory, it has little to no music (leaving the player with only sounds of the machinery and whatnot), some excellently paced scenes, and a lot of that feeling of threat. It's not because the enemy can spawn anywhere at any time (this is actually quite a big con to the other pro's), it's just that everything that happens, the way the monsters attack you and the general feel is that you have to do your best to survive.
Doom 3 isn't particularly scary, although it does rank somewhere on the threshold of my tolerance for this kind of thing. But given that I'm a wimp when it comes to the 'cheap scare' trick (something jumps at you from the darkness, that sort of thing), the game had me pretty scared a few times. Mind you, this is nothing compared to the constant 'shit-your-pants-scary' atmosphere of Dead Space, but it was still enough to make my heart beat faster a few times.
The game isn't perfect though. The lack of a secondary fire for weapons is a trade mark for ID (I guess they do that just to show that if the Unreal franchise, and all the others, do that, it doesn't mean they have to), but I was more surprised by the general blandness of weapons. There isn't one gun which is really fun to shoot, as in Painkiller fun (look up the game and the weapon bearing that name), and even the sounds of firing the weapons are just dry and unsatisfying. Shooting a gun in Call of Duty 2 is so much fun I could shoot in the air just to listen to the rattle of the machine guns. In Doom 3, the primary weapons (Pistol, Shotgun, Machine Gun) sound very dry, you just feel as if you were using a pea shooter.
Also, the game gets a bit boring by the end. A special level you get about 1,5 hour, two hours before the end makes things interesting again, but it ends pretty quickly and you're back to the same thing you've been doing for the rest of the game. Suffice to say, I was happy to be finished with Doom 3, and I'm postponing playing the expansion pack, as I'm pretty bored of this game at this point.
Anyway, the final rating is a 7/10, or maybe more of a 6+/10. As I mentioned before, the strongest element of the game is it's atmosphere, while the rest is either 'ok, but nothing special given today's standards' or rather bland. Still, if you're FPS enthusiasts and for whatever reason haven't played this yet, you can try it out.
One last thing - the game menu features a very kickass track, check it out: