John Carmack Speaks on Doom 3 on GameSpot has a couple of tidbits gleaned from a talk given by id's lead programmer, saying the ability to save the game anywhere on a level is being reexamined, that human characters in the game will be animated with the assistance of motion capture (while most of the monsters will still be hand-animated), and he is struggling with the decision over whether to allow shadows to be turned off in the game, since they are so important to the drama, but they also represent half the engine's rendering efforts. There is also another article on Carmack's talk on GameSpy.