The book has some good history in it and the mysticism is intriguing, along with knowing some of the hidden places and rites it exposes. However, as literature it is long winded and complicated to read, and the language is not used well. It has some good ideas but is not a highlight in the arena of English literature.
I think Twilight has given us a new perspective on how out of control trash literature can get when people start hyping it into something that it isn't. The Da Vinci Code had a pretty insane surge in popularity but it never reached such heights of undeserved acclaim, and while not an amazing book it was certainly a lot better than that trite garbage. In perspective it wasn't overrated that severely.