I agree that most of the time adapting a book into a movie doesn't always turn out so great. Honeslty though, I don't read a whole lot of books. There are tons of books I would have never heard of, had it not been for the movies. It does suck when you read the book, love it, and want a good movie made out of it. But when you go into the movie with no expectations, there's really no harm in having a movie based on a book. If it turns out the movie isn't that great, well now you are aware there is a book and you can read that. Maybe without the movie, you would have never even heard of the book.
My favorite genre of book are those books about dystopian futures. Books like Animal Farm, Brave New World, and 1984 are some of my favorites. These books, for sure, could not been into movies. There is just way too much about the characters and the world itself that needs to be fleshed out, that a book is the best medium. I suppose a TV series could work, but your standard 2 hour movie just won't cut it. Movies generally tend to just focus on the stories of a handful of characters, whereas these books that I read focus more on a soceity as a whole. Specifically, the corrupt leaders that control and dictate what their 'sheep' citizens do with their lives. I suppose this could somewhat work. I'd say Hunger Games falls under this category, but, again, the movies don't really spend too much time talking about the world they live in. It's more focused on Katnisses story. I'm not sure what the books are like, so I can't really say if that's what it's supposed to be like or not.