Soundwave on 04 March 2014
The writer/director himself says the movie is not science fiction:
http://www.entertainmentwise.com/news/142360/Director-Of-Gravity-Alfonso-Cuaron-Claims-The-Film-Is-Not-Sci-Fi-Despite-It-Taking-Place-In-Space
It's a drama, that simply happens to center around two astronauts.
A movie centering around a woman lost and trying to survive in the old American west, but has no real other conventions of the genre isn't necessarily a Western just because of the time period/setting.
