"... although I will note ... that a two-hour movie will not cram the entire complexity of the novel I wrote into its 120-minute running time."

"And that’s fine, and as it turns out, necessary. Movies are not books. Movies are adaptations of books, for another medium entirely. When filmmakers try to make their movies simply a “faithful” version of the book that runs at 24 frames a second, the results (speaking as a former full-time professional film critic) tend to be dreadful more often than not. I don’t want a movie of Old Man’s War that’s a retread of what I’ve already done in the book. What I want is an adaptation and interpretation of what I’ve written that’s interesting and exciting, and is faithful to the idea and feel of the universe I created."

It's been a long time since I saw the LOTR films (and never bothered to see The Hobbit, so I can't comment on those), but, as I recall, that's more or less what Peter Jackson did.