I understand that you can't squeeze the whole book in to a 140 minutes film, but they have changed too many of the things that, to my opinion, make the book great.

It doesn't give the audience a background on the situation, characters, or anything really, and unless you had read the book you won't know where some things come from. I think it would have been a better option to create two or three movies, or at least not to change things that were not necessary to change, to avoid disappointing all the novel lovers!

If you haven't read the book and you like sci-fi movies with visual effects and so on, then you'll like it, that's the reason why I'm giving it a 6, but if you decide to read the book at some point, you'll understand what I'm talking about.