I've only played an hour and a half of this, and have never played DOOM 3 before this, but man, Yahtzee was right when he said "DOOM 3 tripped and hit its head in the dark and forgot that it wasn't System Shock."
I only very recently played DOOM 1 and 2 for the first time on PC and they still felt like really fun, fast, smooth shooters. The same goes for RAGE (the first id game I ever played). DOOM 3 so far feels like an okay (but still smooth) shooter that is also trying to be a first person adventure game.
Do the controls feel smoother and faster on PC? I tried out the XBLA DOOM 1 in this for a bit and it definitely felt slower than ZDoom.