[rrrrrrrrrrrryan]

The books have notoriously rich plots, which is why they were deemed unfilmable.

There was a lot left unsaid in the film to keep it concise and uncomplicated for a viewer like you who hasn't read the books. (Perhaps it was an overcorrection.) The director would occasionally reduce a long meandering sideplot to a quick distrustful glance from one of the characters. Someone who's read the book would pick up on it and feel like it did the book justice by acknowledging those events rather than cutting them out entirely, and the film doesn't burden viewers who haven't read the book with an impossibly hard to follow plot crammed into 2 hours.