[Lawtan]

Well, the setting.
I prefer science fiction, historic, mythological, or fantasy genres. World in Conflict is the best Strategy game (I mean, it is the only one I know of that allows you to setup a squad in a certain member in a building, have the building collapse/fall apart piece by piece, and have "survivors" and "victims" of the collapse.
It's story is also very strong, IMO, and for it to draw me without an ability to build a base, without being an interesting genre, and without it being roleplay at all...it is a pinnacle for its field.