I'm putting myself in a bit of a difficult position here because the more you know about Moon, the less awesome it might be for you. It's important however, that you know you should check it out, so I'll try to tread carefully.
Moon is a bizarre, dark, almost absurd film that takes place—you guessed it— on the moon. The plot mostly has to do with the lone man who's spending several years on there as a glorified maintenance man for some sort of helium mining plant. A lot of it is about him coping with the solitude, but there's a lot more to it than just that. There's not one but two significant twists (though whether the second one is a twist sort of depends on how savvy you are) that by their very nature are difficult to talk around but are spectacular if you don't see them coming. It's a pretty short watch at just over 90 minutes, and it's available on Amazon Instant. Just go watch it, and beware the comments. [Amazon Instant]