The solution is simple: enjoy movies of books you don't intend to read, and avoid movies of books you have read. The Bourne movies and I Robot fall into the former category for me; I have no intention of reading the books so I enjoy the movies on their own terms and have a great time doing so without the inevitable comparisons and disappointment.
If I've read the book, though, and especially if I've loved said book, I know enough now to steer clear of the movie. Because the medium of film is so different from that of the page, it's virtually impossible for movies to be perfectly faithful to the novels on which they're based, and we should not expect them to be. There's the huge problem of compression, not to mention the challenge of putting thoughts into words, emotions into gestures, descriptions into actions. We who have read the novels, however, expect complete fidelity.
Readers create perfect movie versions of novels right there in our heads. We have mental images of the characters and settings, our own interpretations of the actions and expressions of the characters; we know the plot, the sub-plots, all the minor characters by name and dysfunction. We expect to find the whole shebang in the movie. We won't.
There are exceptions to every rule, of course, and stories that shine in both movie and book version exist. My own favourites are The English Patient and Oliver, and I've been told on good authority that The Godfather, Ordinary People, Lonesome Dove, LA Confidential, In the Name of My Father and Silence of the Lambs do too.
Do you know of any stories that excel in both the novel and movie forms? If you do, please share them with us!