I would say that the overarching theme of the movie is: How do you exist/survive in a world where everything that you are (black, female, not-straight) is NOT valued--if not downright despised?
Though people are frank and honest, it's not a depressing film at all and has quite a bit of humor.
Great movie--had action, horror, and a little mystery component.
It's sort of like a grown up episode of scooby doo where the costumed creep running around the mine is really killing people (and the blood/gore flies freely).
I never need to see another pick-axe thrown at me again.