Let me start out by saying that I'm not going to attempt to get into the theology of the book. I remember reading this novel and sighing at how often I disagreed with an opinion, but now that I have read four of his novels, I've learned to separate my own feelings from those of the characters and I hope you will do the same.
There's no denying that The DaVinci Code is entertaining. It starts with a murder in cold blood committed in the famous Louvre Museum. Soon, an American professor is implicated in the crime and the only person who can save him from imprisonment and complete the murdered man's life-long quest is the man's estranged granddaughter. It crosses France and England I wouldn't say no to a "tour the sites of The DaVinci Code" vacation.
The problem that I have is the same as the issue I take with Indiana Jones. Robert Langdon is on a Top 10 Bachelors list and has chocolate-sweet tones and wears a vintage Mickey Mouse watch under his Harris tweed. He is a world-renowned symbologist and on the quest for the Holy Grail. Similarly, Dr. Jones is a knockout who looks good in specs, but also makes women swoon when he brandishes a whip or talks about excavation technique. While both of them are interesting characters, their stories are completely implausible. Just once, I'd like a book in which Robert Langdon would like to find the final resting place of St. Alexandra of Atlantis, but he has to proctor exams and his book tour got canceled, so he's stuck grading papers in Cambridge, Having a PhD in symbology doesn't lead you to having assassination attempts made on your life by Catholic secret societies, just as being an archaeology professor is unlikely to mean that you dabble in the occult with Hitler's goons..
Character issues aside, I read the book with Google at my side so I could cross-reference the works of art described and deciphered. The story drew my attention to elements that I had never considered and I was able to contemplate the interpretation of my faith as well as that of the characters. If you're looking for a stand-out Robert Langdon book, though, try Inferno.