Change is bound to happen since the books are so long and full of detail that would not all fit into a several hour film. The real question is will the change be in size or will it also be in substance. There is a story device called suspense, aka fear of the unknown or as put in Wikipedia "it consists of having some real danger looming and a ray of hope". This is a powerful experience since it plays in our mind, off our expectations of danger and is felt internally.