BladeRunner,. did not stay true to the Book, (Do Androids Dream of Electric Sheep) and despite being a huge fan of the Author, the Movie was MUCH BETTER! (very rare indeed)
One Flew Over The Cuckoos Nest Some who've read it hate the movie, to me this is nonsense, yes a movie is a different genre, it has to be, and this movie is wonderful.
The Shining (weird, both with Jack)
Some more good King adaptations,
Stand By Me
Shawshank Redemption
Green Mile
The Fifth Element
O-Kay, NOT based on a Book, but in fact based on the entire run of issues of "Heavy Metal" Magazines with all of there myriad authors and artists over the decades.
It's simply an amazing visual and atmospheric homage that very accurately portrays the whole flavor of the magazine.
Hmmm.. this is a surprisingly short list,. I'm glad the question wasn't which adaptations to film "sucked"
I'd be typing fro hours.