I've seen some good novel to movie adaptations, but even when hollywood gets it right, you are still likely to lose something in the mix. With a book you can take the time to give the little details, things that enrich the world and draw the reader in. But with a movie it's all business, you have to get that main storyline out within a two hour time limit (usually). The best example is peeves from the harry potter novels. He was a prankster ghost who showed up in nearly every book, but he was cut from all of the movies because he didn't serve any of the stories directly. So, in my opinion, that's the biggest loss when adapting a novel to a movie; the little details that draw you into the world.