Computer & Video Games has the second part of their Carmack interview up for your reading enjoyment. This interview is mainly a tech discussion, however there's a good bit covering some of the elements that will be present in the single player aspect of the game:
We decided Doom 3's gameplay is not going to be some wild innovation - it's a first-person shooter. There are a lot of arguments that can be made about game design, and I prefer simplicity and elegance. There are big arguments that happen inside id over 'do we wanna have an additional control for something like this?', and I'm always the one saying we want the minimum number of everything, because I want it to be simple and fun to play.
By the way, for those curious, this interview is from Quakecon, which took place back in August. And remember kids, disable those cookies!