A Clockwork Orange may have been a better movie than book... that's because the whole book was written in first person from Alex in his future-speak. Tough to sift through parts of it. Still it was a good book. But the movie was brilliant. The movie was very faithful to the book, only omitting one major scene I noticed. Ending was different, though. The book went a few more years into the future, while the movie stopped after Alex was rewarded.
Totally OT, but A Clockwork Orange is both one of my favorite books and favorite movies. I saw the movie several times before I ever read the book, and once you're used to the "viddy this" and "me droogs" that from the film, the book's great. The final chapter in the book gives it the edge in my opinion, because although the book and the film tell essentially the same story, the message is entirely different due to Alex's reflections in the 26th chapter.
Another one where I think the movie was maybe a bit better than the book was "Into the Wild." Or I guess I should say, the movie was a better movie than the book was a book. But again, I like both of those a lot.
Back to Half Blood Prince, I'm bummed that they didn't include the climactic battle at Hogwarts. Just to have the Death Eaters slink off into the bushes was kind of a letdown, because I remember reading those chapters and thinking "this is going to be awesome in the movie." And then nothing.
But overall, I liked the movie quite a bit.