If people expect levels like D1 and D2 + heavy metal music with no story - character development they would be disappointed, it is hard thing to make it in a modern AAA game, because it would sound as a low budget indie game. Just look at the new Wolfenstein, it has cutscenes and character background, the soundtrack features real sounds of the environments, but devs will keep some old school factors.
According to old rumors D4 would happen in earth like D2, but due to graphic limitations of that time, there are few places in D2 that remind earth, most of them had no connections with a futuristic-apocaliptic earth at all.
A D4 would feature a futuristic city in chaos due to hell forces attack, so it would be very different from the simple levels and textures of D2. We would have something like the pictures from an old version of D4 leaked some years ago: a city in chaos, abandoned buildings and cars in streets, corpses everywhere, some survivors trying to fight back like you and of course, featuring a city would be able to make a more open area with a good exploration factor, several ways to follow in order to arrive somewhere, you could walk in streets, explore some buildings, try to explore an abandoned subway etc, you are free to choose the way you want to go to reach the objective.
Off course in this case, real sounds befitting the environments would be more acceptable than heavy metal music all the time.
Putting that aside, I want to see:
- Gore, I want so see the corpses of the demons I killed on the floor, with blood, guts exposed, etc... Monsters that disappear like D3 were boring.
- Hordes of demons in open fields;
- A survival - horror tone but it doesn't mean there can't be action, you can have both action + dark - horror tone at the same time;
- Cool redesign of the weapons, in a futuristic game, weapons must look(I really liked the design of the BFG in DOOM movie) futuristic;
- New monsters, especially big monsters like Cyberdemon - spider mastermind, it would be pretty boring if they didn't bring a new set of interesting and terrifying monsters;
- Cool redesign of the old monsters, ID should hire the guy who made those redesigns of some iconic monsters, I can see them fitting perfectly in D4:
For the pink demons and imps, their desingns in DOOM movie are acceptable for a D4 game.(I love the tires in the pink's back they are better than than the mechanic legs in D3)