It seemed like they softened the character of Robert Langdon (played by Tom Hanks). I read the book with the sense that he was more of a lapsed Catholic--probably agnostic or at least more of a humanist than a religious person. Even though he studied religious symbols, he was academic in approach and not motivated out of personal faith.
The main thesis behind the book is that Mary Madgalene was "the Holy Grail," that she had a baby fathered by Jesus and that the Priory of Scion protected this secret over the last two centuries. In the movie, the Langdon character becomes the one who argues against this theory and when it appears that this is true, he says, "so what?" It doesn't change who Jesus was. This seemed completely against what I remembered from the book, but as I said, I haven't checked back in the book (which I read last year). This just seemed "out of character" for the Robert Langdon of the book.
For me, the book was like any other mystery novel--about the mystery and the search. I think that the movie did a fairly good job of keeping the mystery and suspense.
The bottom line is that it is FICTION. It's a movie based on a book that is based on faulty scholarship.
Here are what I understand the problems are
- the Priory of Scion seems to be a hoax--there were documents that seemed to show the existence of this organization, but it has since been proved that these were not authentic.
- so much of the plot is based on DaVinci's Last Supper and the argument that what was in the painting reveals the secret is based on DaVinci's participation in the Priory of Scion. Since this is not true, it would follow that what DaVinci painted was his own interpretation. The representation of John that is interpreted as Mary is merely DaVinci's representation of a young man.
- the texts that are used to "establish" the relationship between Mary and Jesus are fragments and the interpretation of them stretches beyond reason what is actually in the text.
Here's a link to a great source to find more info and links to more "debunking" http://www.beliefnet.com/story/167/story_16783_1.html
So, if you love a good mystery, read the book (it is better than the movie) or see the movie if you don't want to read. But, know that it is a work of fiction.....
BUT, I have to say that my feminist side, is loving the attention to Mary of Magalene and the opportunity to look at the place in of woman in Jesus' ministry and their place in the early church. Elaine Pagels has written some good scholarly works on this--the Gnostic Gospels and Beyond Belief.