As much as I don't like describing movies with other movies, this one is just too easy: The Blair Witch Project meets The Descent, but with an all-male group of friends. The Ritual REALLY needed better writing because the concept is actually pretty interesting (though not very original), and the visuals are excellent (I mean, it's set in a Scandinavian forest, what's not to like?). Major props to David Bruckner for directing this, and to Andrew Shulkind for the cinematography.
I don't think I've ever been this consistently stressed during a film, beginning to end. All tension, no bullshit. Also, everything else: just wow. I'll attempt filming a review tomorrow, which will probably just be me gushing semi-coherently for 5 minutes.