MOST movies are based on books. A book can contain life. A movie can never contain or recreate life like a book can. I'm happy to see movies based off of books. It sometimes spurrs movie-goers to read. I've noticed a sudden jump in popularity of Lord of the Rings books at my school.
As for movies based on games, people like them because they like being able to recognize things. I've noticed that people enjoy seeing things they have seen before in some other form or fashion. For example, when I watch the Halo movie, I'm going to get a certain tingle of pleasure after seeing some familiar enemies. All of this applies to books as well.
Am I over-analyzing it? Of course I am, I always do. I actually find pleasure in over-analyzing things.
