That can be said for a lot of flicks. I loved the book and loved Kubrick’s interpretation, but I am a Kubrick fan.
One of the best novels ever in my opinion was 'Lolita' by Nobokov. Kubrick made a movie out of it. It was a good and very watchable movie, but just didn't do the novel justice. Same thing with Clockwork orange.
If you like to read and you've never read 'Lolita' I highly recommend it. It makes you think about the main characters mental illness (sickening pedophile) for a long time after your done reading it. Kubrik's version, while good, just doesn't have that effect at all and that should have been the main thing he should have sought after when making the movie.