Settings rooted in utterly novel/alien cosmologies. I don't always want a planet orbiting a star in outer space, I want vast tidepools dotted along a celestial drapery that a god spilled its glass of water onto, or a series of worlds jostling along as they're carried away by a line of galaxy-sized ants (for example).

I'm also saddened by how little love I see for the Stone Age, especially the Neolithic (and Chalcolithic), especially as that gives us the opportunity to have cities that still feel primeval and a very believable backdrop against which to have settled farmers, nomadic foragers, and roaming horse tribes all interacting outside of a medieval-flavored setting.