I saw this movie a month or two ago. After the movie, my friends and I were discussing the ending and things we didn't like about it. I haven't read the book yet, I'm waiting on my roommate to relinquish the book so I can give it a go.
Evidently there's an alternate ending. It's not much better, it doesn't quite mesh with the book's theme, but it's better than the original. The link has some interesting theories on why this ending wasn't used, though I'm not sure I agree with them. Either way, the alternate comes out better.
(Tip: if you haven't seen the movie, go watch it first)