I was too tired to post a normal review of it after I saw it Saturday night, so I'll just throw it in here.
Summary: Two guys, Lawrence and Adam, awake mysteriously in what appears to be some sort of ancient rundown bathroom, finding themselves chained to pipes on opposite sides of the room with a dead guy laying in the middle of the room. They both a cassette tapes describing in some detail what their "mission" is to complete to survive. However, many unforeseen events occur in the midst, changing the entire perspective of the situation.
Pros: Amazing plot twists and a great "fuck-with-your-head" feel the entire movie.
Cons: Lots of flashbacks may be slightly difficult to follow and a few clear instances of the cliche "stupid-decisions-because-it's-a-horror-flick".
Overall: 5/5. Expecting it to be a typical horror movie, I was quite impressed. I didn't feel it had the "horror" that The Grudge had, but the mental suspense was abundant and it was a much better plot/movie overall. And along with what Shawn said, nobody will EVER see the end coming. I don't care how good any of you folks have been at seeing the outcome a mile away, but this movie will end your streak.