Dan Brown is probably the worst author I have ever read. If he had "written" a book without such a controversial topic no self-respecting publisher would ever have touched it. Given his literary skills, Brown should be working in McDonalds not earning millions writing terrible fiction. I haven't seen the movie, but maybe the screen writer has polished the turd that is Brown's command of the English language.
As for the so-called historical facts that the book is based on, and the so-called "history" presented in "Holy Blood, Holy Grail", the fact that people believe and give these books any historical credibility is hilarious. Good history and credible history is not based on guesses or hoaxed "secret organisations" like the Priory of Sion.
It all just goes to prove the world loves a good conspiracy theory.