Powered through the end of Doom 3 the other day. While the major flaws I mentioned earlier wound up persisting throughout the whole thing, I'd rate it an enjoyable experience overall. The environments did wind up getting some variation by the end, with Hell being creepy-cool, and the lowest base areas reminding me a lot of the vitrified testing chambers from Portal 2. The story presentation was an interesting attempt to take the classic bare-bones "kill all the demons!" premise and re-cast it in a more plausible, grounded light...I wouldn't give it any awards, but it got the job done. One little element that stood out in a positive way was the environment interaction: instead of the usual "press E to do everything" command, your crosshair turned into a cursor when interacting with a touchscreen in-game, and it felt really seamless and immersive.
Now I'm working on the expansion, and oh jeez...they've managed to take the Gravity Gun and eliminate just about everything that was so intuitive and graceful about it.