Given that the book takes 20+ hours to read and that an author can jam a lot of detail into a few words colored by the reader's imagination, there's not much you can do in 2h30m to faithfully reproduce that. If the movie had been 14 hours long, a 'Lord Of The Rings in one bite', those who panned it here would have praised it.
Alas, you can't have everything; where would you put it?