I wasn't impressed. Underneath the metaphysical trappings of an author who's discovered the stories of the Priory of Sion and decided that they're a truth that needs to shake the Catholic powers-that-be lies a run-of-the-mill technothriller, reminiscent of the myriad of Clancies and Cusslers that, err, grace the airport bookshop shelves. It's probably a good thing that I was reading it on a transatlantic flight with bad movies, otherwise I'd probably have watched the films instead of reading a second rate thriller.
The Da Vinci Code is certainly not the ground-breaking novel that its die-hard fans make it out to be - if anything it's just retreading ground from The Holy Blood and The Holy Grail and Katherine Kurtz and Deborah Turner Harris' The Adept fantasies. There's more semiotics and codebreaking in any one of Eco's novels (or even Jasper Fforde's comedic literary fantasies), while 1970's BBC documentaries told more about the Priory of Sion and the art of Da Vinci than Brown's novel. There's also so much missing here: no mention of Rennes-Le-Chateau, Bannockburn or the paintings of Poussin. It's a half-baked work that promises much more than it delivers.
Not recommended at all. And my sympathy goes out to the caretakers of Rosslyn Chapel...
(and why does the geek in me keep typing "The Priory of Psion")