I may be wrong or misinformed, but Doom3 is going to be fairly low poly compared to HL2 and current Unreal tech. It'll still look decent because the shadowy per pixel lighting and semi-realistic settings don't need as many polys. If you're just going to make a flat wall you don't need that many polys. Then when that wall is mainly hidden in a dark shadow because of per pixel lighting, you don't need the extra detail to make it interesting. There's no point in having huge amounts of poly detail in a game that's mostly hidden in the shadows.