The perfect ending. *spoilers obviously*

I don't think it's "out of nowhere". The boy finally decides to try to escape and injures him. The car crash is not a "deus ex machina", but a result of the attack: we can see that Michael's face is burnt, so his vision is likely to be affected too, and the accident happened at night.

The only thing I found unrealistic was the "prison" door, which was easily recognisable as such, and right next to the stairs. Why didn't he hide it better? What did he say when the gas/electricity man came to check the meter and asked "what did you lock in there"?

My problem with the ending is that it seems like a pretty sadistic little joke to play on the audience, to make it wait and wait, knowing the boy is locked up in his cell alone day after day. We can't be sure if his "pantry" had been recently stocked or not--It could have recently run dry and the boy could be going hungry.

From the dialog, we learn that Michael's funeral is on a Tuesday (which would have been at least four days after he died.) After that his mother says she will go to Michael's house to clean it out the next "weekend," tick, tick, tick... They get there sometime that next weekend, do all sorts of stuff before the mother goes to the basement... Then she LEAVES the basement without opening the door to the boy's "cell". The director keeps up with the slow paced scenes of the brother and mother cleaning out the house even after that before she finally goes back down and finally opens the door.

We, as audience members become more and more upset throughout this last 15 minutes of the film at the thought of the boy going hungry, at least I did. It's very Hitchcockian, actually--slyly humorous in a droll, black comedy sort of way But for a movie that seemed to be very serious minded about confronting "evil" itself to end with such a cheap, sadistic little waiting game being pulled on us, and then not giving us proof one way or the other about the boy's fate, was really disappointing to me. I would have given this very troubling, well-made movie an 8 or a 9 on a ten point scale, but after that sophomoric ending, I dropped it to a 7. Just my opinion.

Yes, I was disappointed for the ending too, the first hour was slow and boring and plain to me, the last half was interesting, the last second was quite a failure, it is like a unfinished job, too hasty to end. Leave us imagination? then we don't have to watch any movie, no Harry Potter or such.

Better to end it with any result, good or bad, it is a duty of the filmmaker, at least to some of the audiences, my $0.02.