Movies based on books usually tend to cut a lot of the really juicy characterization out, simplify the plots beyond belief, and generally end up looking very little like the books they're ostensibly based on. Comic books and game adaptations rarely fare better. That being said, we now live in an age where a few shining examples (Lord of the Rings, The Dark Knight, V for Vendetta, etc.) have shown us that it can be done well, so I'll play along.
Hands-down one of my favorite books is Warchild by Karin Lowachee. I would love to see this one made into a movie. It has the outer trappings of a space opera with a conflict between humanity and the alien strivs, but it's really more nuanced and character-driven than most titles in the genre. Of course, I have a feeling that the things I love about the book would probably get lost in translation. The asexual protagonist would probably get a female love interest jammed down his throat, the subtlety of the conflict between humans and aliens would likely be eliminated, and the Big Bad would probably lose the defining trait that makes him so bad, if only because it's rather uncomfortable. Done right, the book could be an awesome political SF, but done wrong it would just be another Star Wars knock-off. So I take it back, I don't want to see it adapted.
but i shall hush in case if spoiling it
