Gamespy has an interview with Robert Duffy who is the developement tool coder for Doom III, where he explains a few interesting things for modellers and mappers looking forward to producing things for this engine..
"In Quake 3 a model may have two or three thousand polygons, whereas the player models in DOOM III, the original art has probably close to a million polygons. That's been reduced down to four or five thousand for in-game use, but you have to have that million polygon model - you have to have a lot of polygons to generate the bumpmap data that makes it look like a high-poly model in game...you can set the two next to each other in-game and you can barely tell the difference, because of the bumpmapping and specular effects, etc."
and texturing...
"A large percentage of the textures are done exactly the same way. They'll model a wall at a very high polycount, and then renderbump it and turn it into a bumpmap set, into a set of textures that all combine together to give it the 3D look."