I don't mind id trying new things, they always have before and they're not exactly a team to stay away from the ballsy calls but what I would really hate, to the point of me not even trying the game, is incorporating lots of 'modern shooter' tropes into the game. Not for the sake of it being 'retro' or anything like that but alot of the modern shooter mechanics are conflicting with what I consider Doom.
Two weapon system? Great they've just managed to svck all the fun out of the weapons by removing the metagame of picking the right weapon for the right type of enemies as well as restricting your gameplay options by controlling the weapons available
Regenerating Health? Yeah it's not like the levels in all previous doom games have been fantastically designed as a war of attrition against the players health, now it's just a case of trying to overwhelm the player with each individual encounter and no more frantically running around in the dark hoping you come across a medkit before your next encounter.
Intrusive Exposition? I didn't replay Rage at all until I figured out there was that scenario mode in the scorchers DLC because there was no way in hell I was going to sit through all the dialogue (that I had already experienced and now knew the story) and crap quests to get to the real missions. Despite quite a few of them being some of the best fps encounters this generation IMO
Skinned fetch quest objectives? They're just a way of making the player traverse the same environment after they've reached a certain point. If you're going to do it (and lots of games have done it well in the past) have some balls and don't hide it behind some forced exposition. Even Doom 3 (which had a much more focused approach to the narrative) wasn't afraid to just say "nope this door is locked go find its key".
Objective Markers? No FPS should need them, it just covers up for poor level design. By all means they should have a hint system if they think it needs it, but make it optional and not always on the screen.