Until I saw this in a second hand bookshop I hadn't realised the film was based on a novel. It is certainly true that there isn't much in the book that that you won't have seen in the film. In fact one of the things that struck me was what an easy job the scriptwriters had. The key events and dialogue are all here.
But if you enjoyed the film there is no reason you shouldn't enjoy the book, though it probably impossible not to imagine Hoffman, Bancroft etc. as you read.
Benjamin Braddock is a memorable, engaging an infuriating character, the story is both funny and and moving. I think without the slick images and direction you focus more on the characters and themselves.
A good read in itself and a fascinating backgrounder to a major film