It could be a theater piece too. There is not much of location changes and the end of the world suspense feeling is underlying. What really is at the heart of this movie is the relationships between the characters. It's also looking at gender and what special circumstances might do to somebody.
While this character study in the disguise of science fiction movie, it doesn't work all the time. Which is not entirely the casts fault. The script could and should have been a bit wittier and have more finesse to it. I generally like Spanish (language) movies and this had the makings of something bigger (budget restraints might have played a role) but this is undercooked.