I've got Doom III and been playing it for a while now. The graphics are good, but the gameplay is a bit crap. Plus some of the levels are a little repetitive in a few places, so it's easy to get lost. And why is most of it in the dark? Fortunately I installed a patch that attaches the flashlight to most of the guns, making the gameplay a whole lot better.
The multiplayer option is sort of fun, since me and my buddies played it over a LAN conneciton last night, but it's nowhere near as fun as Unreal Tournament 2004 or Half-Life.
But it doesn't mean I'm not enjoying Doom III so far, though, 'cause I am.

Overall it's a good game even if it leaves quite a lot to be desired, and lags heavily in places, even when set on the 'medium' quality setting, on my powerful Althon XP 3000+ with Radeon 9800 Pro and 512 RAM computer. It has NPC interaction, okay phyisics, loads of zombies and strange creatures to shoot, and also it includes loads of bizzare and gory scenes. Plus it's really cool how in-game computer screens and monitors are readable and useable by moving your cross-hair over them.
Still, I think Doom III wasn't as good as I thought it would be, and my expectations for it were pretty low. I'm still a devoted Half-Life fan. Half-Life 2 SHOULD be here soon, I hope, and I'm pretty sure that'll kick Doom III right up the arse, except in the graphics department. But like I've said before elsewhere: Graphics don't make a game.
- DH
EDIT: BTW, this review on Gamespot pretty much sums Doom III up:
http://www.gamespot.com/pc/action/doom3/review.html