what a book gives u (specially in adventure books) is the power to imagine the world the author's describing, it also gives u sleep (i read Lord of the Rings books b4 i go to sleep, makes me sleepy so deghreh beghfa
) well anyways it's nice to do both, they each have their advantages and disadvantages.
PS: a book also gives out more Info than a movie (loads more to help u comprehend the story, which i'm sure helps the ppl workin on the movie of that book
)