The Bible was written by man over thousands of years, more than 2,000 years ago. Is it possible it could've been changed or altered, important sections lost or rewritten over the centuries? How do we know we're getting the entire, original story? Who is to say that the Bible as we know it today includes all the accounts that were originally written? And how do we know the stories that do survive haven't had parts omitted or censored? Is our belief in God based on false doctrine? 
 Everyone loves a conspiracy, and what better conspiracy to investigate than one that involves the whole world. There are so many historical citations that this may as well be a history textbook. Not many stories can get away with that, but the information is so interesting you will believe every word of it. ...because it makes sense. 
 All the symbolic, artistic and historical references make this possibility totally believable. Everything about the catholic church censoring the Bible to keep itself in power makes perfect sense. Undeniably the Church resorted to extreme means to keep itself in power in the Middle Ages. Could they have altered the Bible itself, too? 
 But how much of The Da Vinci Code is fiction and how much is fact? If you buy into the conspiracy, Robert Langdon's ability to find hidden symbols in everyday life reinforces the elaborate lies we've been told. The lies about sexuality, the female gender, male superiority, and the real origins of the pentagram and the goat (they weren't always Satanic symbols, but thanks to the Church they have become so). 
 If you don't buy into the conspiracy, it gets far-fetched and annoying. Everything is a symbol to Robert Langdon. Maybe he'd like to look for a goddess symbol on a box of cereal. Isn't it possible that sometimes a triangle is just a triangle? It doesn't always have to be an encrypted symbol for the womb. 
 It's a mind-blowing concept, but only if you allow yourself to believe this could be possible, and accept that the story is just an excuse to present the concept. Really, this book is not suspenseful, nor does it tell a particularly well-executed or original story. There is no code hidden in the works of Da Vinci that Langdon must decipher to learn the deep, dark secret. The characters are following a trail of clues laid out by the man who was murdered in the first chapter. And at the end of the trail is something just a wee bit disappointing. Langdon doesn't learn or discover anything along the way. He already knows about this conspiracy, and we discover it because he lectures it to the reader. It would've been better if he discovered it as he solved the clues, making the conspiracy part of the story instead of the excuse for it. 
 The Da Vinci Code is a lecture, but it's interesting enough as is because the idea behind it is so mind-blowing. The concept triumphs over the story. There's nothing wrong with that, but hopefully Da Vinci Code 2 won't rely on it. 
 I did a book/movie comparison on my blog. Check it out.