Earlier I was thinking about genres-- and not about reading different genres, but writing them. All genres, like fantasy, dystopic, contemporary, and et cetera share similar, crucial components. They all should have a gripping plot, an interesting voice, and believable characters. The setting is usually the main thing I see setting genres apart. (That and the fact that some fantasies and scifis have bizarre names.)
By setting I mean more than just the backdrop-- I also include the boundaries of the fictional world (e.i. magic or space travel and whatnot). Therefore, the biggest different in writing one genre to another is the amount of explaining required.
In my experience, writing a contemporary requires the least explaining. I don't mean to say contemporaries have little explanation-- there could be explanation as to how belays or trapdoors work, or the setting-type explanation about how the nooks and crannies of a ski lodge hide secrets or the expanse of an Oregon beach is actually the perfect meeting place for a rookie con artist (just off the top of my head). However, for a contemporary, I like to classify those sorts of explanation as 'description," because they fall within the boundaries of a world readers already understand.
Writing a scifi or fantasy or dystopia requires more explanation-- new world boundaries, created phenomena, "impossible" locations. When writing any of these it's easy to go in circles with explanation. I always make sure I understand the basics of my imagined setting before I try to explain its way onto the paper.
Just a few thoughts on explanation vs. genres. What differentiates between genres for you?