I think one of the most common heard phrases after a movie based on a book comes out it is "The book was much better."
The truth is that is probably the way I feel most of the time. There are exceptions of course.
1. Jurassic Park. I saw the movie first and read the book shortly after. Michael Crichton is definitely a hit and miss for me and this is mostly a hit, but it's only a good book while I would argue that the movie is a four star plus.

2. Casino Royale although I admit that's a little unfair given the time in between release of the book and the movie. The book is good again, but the movie is one of Bond's best.

3. The Godfather. The book is at best a good story and that may only be because of my deep love of the movie. Compared to the movie the book has deep flaws.