I enjoyed the first 30 miutes of Doom 3, some of the most atmospheric, freaky gameplay of my life. But it soon became repetitive, dull, and obvious even.
The gameplay is uninspired, with triggers and spawns which were used to effect 10 years ago, but you don't see so much of now (for a reason). The overuse of blindly shooting in the dark is another (in my opinion) bad design flaw. Used sparingly it could've been very effective, but with the overuse it gets it quickly becomes annoying.
I didn't finish Doom 3, it sits on my hard drive, but there is no pull back to it. I feel I will just be repeating the first three hours of gameplay over and over, and that isn't appealing.
A good tech demo for a great engine, but as a game? Meh.