Dan Brown: Great fiction -- pi$$ poor research.
I never got passed the first Mission Impossible...when they had the original character turn.
Specifically referring to The Da Vinci Code, I'd say it's fun, but not great fiction. It's more like the less well known The Avenger books by Kenneth Robeson, who did the much more fun Doc Savage pulp fiction stuff in the 30s. Pure pot boiler stuff. Like The Avenger books Da Vinci has badly drawn characters, is internally inconsistent but with fairly well done scene depictions. In fact, the best thing about Brown's Da Vinci Code is his place descriptions. He has a good eye for architecture and is competent at conveying that to his readers.
I'd also go beyond "pi$$ poor" all the way to fraudulent to describe his "research." He's not even up to Von Daniken.
If you do enjoy things like Da Vinci I'd recommend Focault's Pendulum, by Umberto Eco. It's tough to get through the opening 50 pages or so (nowhere near as tough as his Name Of The Rose), but well worth the trouble. It covers many of the same themes and even some similar locations to Da Vinci Code. I also heartily recommend The Adept series by Katherine Kurtz and Deborah Turner Harris. First, I absolutely fell in love with their descriptions of Scotland, including a much better description of Rosalyn Chapel than Brown manages. They also provide much more context about both the real and imagined history of the chapel. I also enjoyed their heros much more than the rather pathetic characters that Brown gives us. If you read these books I think you'll really like Dr. Adam Sinclair. I've always thought it would make a great continuing series of movies for someone like Pierce Brosnan. Oh, and they're basically on the side of believing in God and Christ, not against Them, as I think Brown is. They do, at least, embrace the supernatural in their stories (some of it in the first book is a little silly, but still very much fun).
They even have a spin off pair of books which explain what REALLY happened with William Wallace and how Robert The Bruce became King of a free Scotland.
What research ? It's fiction for God's sake. Or not for God's sake.
BUMP
Piss poor writing as well.