HomeLAN got a chance to play the Doom III deathmatch demo that’s on display at QuakeCon. The four player deathmatch took place on a level co-designed by id Software and Splash Damage.
The Shack has also posted a couple of screenshots that look kind of ok, but don't show off much of the eyecandy.

I'm not so excited about what is being shown at QuakeCon given that is multiplayer gameplay only (which IMO is getting more generic, or perhaps I'm just jealous given the lack of a fast enough net connection), in any case, I expect Doom III to shine in the single player area more than anything.