Hmm.. Movies based on books, from my experiences, aren't really all that great compared to the books.
The HP movies may look all spectacular and stuff, but the books have so much more depth and left out scenes and stuff. I haven't seen them all, though. Nor read them all, either.
Although I DO prefer the movies of the Bourne series. It's way different than the book series, but it's done much better. I mean.. in the book series, Bourne is an old man... jumping off roof tops. That's like... no.