Lots of my favorite books have been turned into movies, but my favorite film adaptation is:
No Country for Old Men by Cormac McCarthy (book, film)
Never in my life have I seen such a true adaptation. I read the book and loved it; I saw the movie and loved it. I don’t like everything they do, but the Coen brothers blew me away on this one. Watching the movie actually feels like reading the book— Cormac McCarthy’s descriptions of landscape and mood translate perfectly into a visual masterpiece. The book is not a happy one, but it is mesmerizing; it has a bizarre storyline and even more bizarre characters, played flawlessly by Javier Bardem and Josh Brolin. I highly recommend both book and film.
Curious about the rest of my answers? Find a list of them here.