I actually feel the opposite. The story in the film is usually a condensed version of the story in the book, so the book offers surprises and insight that the film ignored or merely hinted at, while the film is likely to disappoint if you are already familiar with the book. There are exceptions of course.
truth but i feel like the buildup and the nuances in the book, which don't mean as much if you already know what happens because you already watched the movie. (exceptions apply)