I watched this movie on the plane the other day, trying to find something to keep me awake (as sleep on an airplane never leaves you rested, but merely with a stiff body).
What I saw was, however - to my positive surprise - much more than just something to pass time, as I actually enjoyed it a lot.
I find the plot quite fascinating and very original, and it has, with its unpredictability, more than just a few surprises in store. Granted, there are a few inconsistencies with the storyline, but I didn't see them as a big problem, as the movie, as a whole, works.
All in all, a really good horror thriller, which keeps you guessing till the very end.