After thinking about it for part of the day I would like to see someone make a game that combined gameplay elements from Splinter Cell, CounterStrike, Call of Duty/Medal Of Honor, Far Cry, and Half Life, etc with everything destroyable, all buildings usable, all vehicles usable, and no linear gameplay. Levels could have several smaller objectives that are optional to complete to reach the main objective of that level. Each optional object you complete makes it easier to complete the main objective. Give me different options to complete a level, I'm tired of the "run here, go to the third floor, find the anti-tank gun, run down 1 flight of stairs, shoot at tank and then die" only because you where too slow running up or down the stairs.
One thing I always hated about FPS games like Doom was you spent a freaking hugh amount of time running around looking for key cards to open a door. WTH!!, I'm a walking doomsday machine carrying rocket launchers, several automatic weapons and explosives I should be able to just blow the damn door off its hinges, shoot through walls, etc...