I read the book Deliverance. Between the movie and the book I was completely influenced by the movie; having seen it long before I read the book.
The movie, I thought, followed the book very closely, except that there was much more background information in the book, and of course characters I could not relate to as deeply because Burt Reynolds, Jon Voight, Ronny Cox and Ned Beatty are stuck in my head, and as a result the characters in the book seemed a little lack-luster, a little duller, but had I read the book first I would probably have believed that the movie characters were overacted.
All in all, though, as far as following the plot I thought they did a good job, and I like that the author (James Dickey) played the sheriff in the movie.
YouTube Preview: https://www.youtube.com/watch?v=at-gOm93fZg