Salman Rushdie directed a film based on his novel Midnight's Children. He is quoted as being 'very proud of this film'. From what I could tell from the trailer, it looks as though the director has chosen to create a tale of social realism, laced heavily with moral message. It looks as though it cannot hope to convey the metaphorical complexities of the novel because even though it may dramatise them it cannot state them. This goes to the nub of why film differs from books: a writer can dictate to a much greater extent what the reader/viewer thinks and feels, how much he understands. A writer gets to impose his vision exactly, simply because he can elucidate it verbally.
Film can only show, not say. But the moment an author 'says' anything, the work is dead.
Why the Real 'Directors'