The worst part about this one was the pacing, but then the book suffered from similar problems. I wish they hadn't messed with the ending though. It would have been nice for them to keep in the part where Dumbledore breaks down the prophecy for Harry and to explicitly show that Trewlaney was the one who made the prophecy. I think the prophecy needed to be played up just a bit more. It's a pretty central point in Half Blood Prince.