I like identifiable usable worlds to play around in. It's sounds silly but phones, light switches, fire hydrants, TVs, toilets, pool tables etc are a blast for me. Nothing against the Dooms and Quakes out there but you spend those entire games in some generic alien world that have NOTHING but generic alien design and bland window dressing.
This! I liked D3D because it gave me the opportunity to play in a believable level from a first person perspective. You could wreak utter destruction in cinemas, shops, on the street... Naturally, generic bland "dungeon" levels are the easiest to make because you can just paste the same two textures ad infinitum, whereas a believable world takes some handcrafting, with each zone being unique.