While visiting Greece I finished Charles Portis' True Grit.
It is as similar to the movie version - both movie versions - as any novel I have ever read. I can only imagine that the Coen brothers and Henry Hathaway before them must have taken the novel and filmed it page by page. So having seen two extraordinary films, both very similar, what did I gain by reading the book? Is there anything more to it than just another "version," as if someone filmed True Grit yet a third time, with John Travolta as Rooster Cogburn and Adam Sandler in drag as Mattie?
The reason the novel will always be different - if not always superior - to the movie is because the novel gives greater intimacy with the characters.
Alfred Hitchcock said that whereas the stage is objective, film is subjective. What he meant is that film can suggest the interior experience of a character in a way that a stage play cannot. If two characters kiss on stage, we witness it, and that's that. In a Hitchcock film, we see a close up of Jimmy Stewart's face. Then we see a shot of Grace Kelly, from Stewart's point of view, coming in for the kiss. Then we see her brush her lips against his. Then we see Kelly's face again. And last Stewart's reaction. The sequence of shots give us the illusion that we're right there with Jimmy Stewart getting smooched.
But even a master like Hitchcock can't tell you what goes through Stewart's mind. When you write, you can't help but tell how to think about it: even choosing a synonymn for "kiss:" brush lips, smooch, kiss - is going to inform the reader how to feel about this transaction.
The stage is objective. Film is subjective. The written word is subjective to the second power.