I agree with some of the comments in this thread--the LotR movies were better than the books, although this is just my humble opinion. The story was captivating enough for me to get through to the end (some of my friends gave up), but I really had trouble following his "old" English style, and it was quite a struggle for me complete all 4 (trilogy + Hobbit).
However, such cases are rare. Books in general are better than movie adaptations, at least the ones I've read/watched.
True, but lets just say it's very, very, VERY rare.
In my experience, it also matters which you saw/read first. Like, when you read the book first, you have a certain image of the characters in your head, and when they look completely different in the movie, you might end up not liking it.
When it comes to book-to-film, I'm happy when the films are as good as the book was. You know, not like friggin Eragon. As a scriptwriter/director, screwing up your movie is bad, but it's somehow worse when you started from a decent book