Your mention of "Jaws" is interesting. I haven't read the book but liked the movie a lot and wonder if it isn't an example of the Hollywood truism: "Bad books make good movies."

The classic example is The Godfather. Everyone agrees it's a great movie, but when I went back to reread the book (after having torn through it ages ago), I couldn't get through it. Some movies raise to a higher power the books that inspired them.