As cool as adaptations would be if they were pretty much word-for-word from the book, they can sometimes be more boring that way. Like, halfway through the movie the whole "wow this world I imagined is coming to life" thing would wear off and you'd just be like, "But now I already know what happens."
Which is why it's cool sometimes to have movie adaptations that kind of take the same spirit and concept of the book in a slightly different direction. That way it has the same charm of being the world you imagined, but it's different enough to not make you feel like your imagination is being subverted.
But then you have movies like The Lost World, which take things in a way different direction (T-Rex in the big city) and don't remain true to the spirit of the book, and take the concept in a totally ridiculous direction and just generally fuck everything up.