A philosophical horror film A good (and depressing) movie if you want to sit and ponder the futility of everything, but not so great if you're just seeking a Saturday night scare-fest. That's a problem, because it's terribly mis-marketed - the cover and blurb pitch this as a slasher film when it's definitely not.
The film raises a philosophical question for viewers to chew on: does anything we do ever matter if everything we do will be forgotten almost as soon as we're gone? (One character even spells this out as he tries to leave a mark that can't be erased.) The horror here isn't a killer that can be defeated, a monster that can be escaped, or a conspiracy that can be unraveled and explained away, but the inevitable fact of death and our own eventual irrelevance, the fear of being erased by time. Like a post-modern danse macabre, each character acts a symbol (of evil, of family, of education, of religion, etc.), though it's disturbing to wonder if our sympathies would fall differently with a bit less B-movie scripting and a bit more A-list acting.
I didn't particularly mind the open ending or the lack of explanations, because the question the film is poking us to think about has no objective answer. I doubt any concrete explanation the film could have cooked up would have worked without undermining that central question and turning the film into the straightforward slasher the cover advertises.