Overall, this is a very strong and disturbing thriller. The opening scene draws you in, making you want to know just what the heck happened at that party. When you learn the truth, and see more and more horrible things happen, you can't stop watching. I didn't see the twist at the end coming, it was fairly well written, although, toward the end of the movie, things kind of fell apart a bit and got a bit too ridiculous.
But, that's just the very end of the film, and everything leading up to that point is very strong and well done. The boys are very good in their roles, and effectively creepy in a quiet way.