I hope DooM 4 doesn't turn out "DooM 3 in a city". Whereas first 2 DooM games were action shooters, with multiple enemies and paths, the 3rd one is a dark corridor game where every single fork in the road has a correct path and a blocked path. With constant scripted sequences reminiscent of pop-ups. You hardly ever face 5 monsters at a time. They also seem dumber than before, they can't even open a door. They've managed to make darkness tiresome instead of scary.
In short, I hope for a game more like Serious Sam, or Painkiller, but with more interesting and varied enemies and levels.