Sci-fi in general I find is at its best when it melds multiple genres together. Sometimes the meldings which seem really out of left field end up making for really memorable stories.
In general, I love stories that blur (or trash) genre boundaries. Weird westerns. Vampire pirates. Sci-fi murder mysteries. Time-travel romances.
Mixing and matching genres is one of my favorite things, actually.
And this is where I shamelessly mention co-editing two anthologies of science fiction vampire and werewolf stories for Baen Books back in the day, titled Tomorrow Sucks and Tomorrow Bites, respectively.
We flirted with doing a third volume of SF zombie stories, tentatively titled Tomorrow Stinks, but, alas, we never got around to it.


