It is great to read a book and then watch a movie based on it.
I favour the order particularly. A book is an insight into the writer's mind. It is full of details, explanations and a great deal of elaboration. The writer has the liberty to proceed at any pace that the reader finds suitable.
A film maker on the other hand is constrained by time. He has to use pictures and actions to convey the same emotions that a writer uses words for. The idea has to be evident to the viewer without any elaborate explanation.
A book leaves a lot to the imagination of the reader. Though writers do create the entire setting, it is all upto the reader to imagine the place, the exact features, the clothes, the emotions, the colors! And readers generally do a good job.
A film on the other hand constricts the flights of the mind by forcing it to accept things as they are portrayed. There is very little work for the mind, except perhaps listen to the dialogues carefully.
I recently was watching the movie 'The Fourth Protocol'. I absolutely adore the way Forsyth has created a web of mystery around the story of a middle-aged MI5 agent versus a suave KGB Illegal. So a comparison with the book was inevitable.
There were no Jim Rawlings or Billy in the film. The brilliance of the theft in Berenson's apartment loses its charm in the film. All the details of how Rawlings works with the skeleton key, works his way with the alarm system, of Billy's excellent work the previous evening and the use of CLC and water as the shock absorber vanish in thin air. I am sure anyone who has seen the movie without reading the book has missed the relish of a mind-blowing robbery.
Then the excellent ferrreting in Pretoria to discover Jan Marais, constructing the nuke by breaching the Fourth Protocol, the entire stint of tying the goat and waiting for the tiger, they all vanish into ether in the film. Michael Caine is good, so is Pierce Brosnan, but the flavour of the book is lacking in the film.