I would love to fight in a bleak ruined city filled with collapsed buildings. There would be so many corners you would be afraid to turn around. Also, if the color pallet is greyish it would bring out the colors of all the races and explosions really well. Like so?
Fighting through a Hive City has always been on my mind...although fighting through a Tyranid/Chaos infested landscape (Or both!) would also be really dark and enjoyable.
As long as it isn't star wars where every planet has only one type of terrain...but I don't believe any of the races treat their environments particularly well, so to see the negative impacts each race has on the terrain as they control it would be pretty cool. Imperium of Man - toxic dumps, deforestation, large strip mines, plumes of ash and smoke from manufactorum, turning the native population into twisted subhuman mutants Chaos - tainted land all evil and twisted looking, turning the native population into twisted subhuman mutants Orks - Orky workshops with scrap metal/chemicals just lying around leaching into ground water turning the native population into twisted subhuman mutants...slaves Eldar - actually probably not much of an impact, but subhuman mutants anyway Also boarding actions on enemy ships! (with subhuman mutants that live below/inbetween decks) Hmmm....mutants as a playable race?
Hive cities or torn apart, rocky terrain full of gorges and ravines, something like Black Crag in Warhammer Online - claustrofobic, tight and packed, ideal for barrage fire and some explosives.
Space ship interiors building interiors hive cities mountain passes (lots of verticality, oppressive dramatic set pieces) TRENCHES and front lines.
