Go back to DOOM 1... look at some of the outdoor maps.. especially in Episode 3... the terrain of hell, the bluffs and red skies... the rivers of blood and fire, the sick and twisted flesh and intestines, dark roughness and rocky grounds of Mt. Erebeus. The vast landscape of mountainous region and nightmarish vistas and cliffsides/flats that they really tried to emphasize as best as they could using the technology at the time.
I think the outdoor enviroments for places like phobos, deimos, hell, earth... thats going to really play a giant part in it. Combine that with the AI, modelling, and alot of lightning options, and on-screen model count... I do beleive may have a DOOM that really drops our jaws today like the DOOM's of 2 decades ago. Not that DOOM 3 wasn't jaw droppingly gorgeous... but i think DOOM 4 will stay more true to the style and gameplay of the originals than the action horror halls of DOOM 3.
id tech 5 and RAGE really do show the potential for these sorts of things going forward.