Like the book, The DaVinci Code isn't a particularly good murder mystery but keeps you interested. Director Ron Howard reveled in a large budget, which is too bad. A slightly sparser movie would have been better, maybe. Too much moving camera and not enough of the neat hologram-like effects which do an excellent job with visual exposition.
If Opus Dei wants to whine about their treatment in the movie, they should also take up the cause of the Jews over The Passion of the Christ. The movie's historical facts are, to my knowledge, on firm ground: Constantine not being baptized until his deathbed, the Knights Templar, the Albigensian crusade, etc. Historically, you can probably ignore the stuff about The Priory of Sion without hurting the basic thread. I was vastly amused at how the movie shoots down the major objections to the book. As the characters say at various times, telling the real history does NOT take away from your religious beliefs or from the example of Jesus. Indeed, says the movie, setting the record straight is what he would have wanted. Please keep in mind that it's fiction, and the first word you see on the screen is "Imagine" (part of the logo for Imagine Entertainment).
While I don't know if Opus Dei trains albino killer monks, their history is even screwier than the movie gets around to. The self-flaggelation and use of the cilice is real. I'll let others go into greater detail.
Meanwhile, the symbolism that Robert Langdon (Tom Hanks) talks about is handled very well. You do get a sense that paintings and sculpture and even architecture have more than utilitarian purposes. Howard handles this aspect of the book extremely well, even as he takes shortcuts to pare a lot of exposition into a 149 minute film.
While the backstory is faithful to the book, I can't help but compare the "origins" of Robert and Sophie to those of Batman and Harry Potter. I better stop.
I just came back so may change my mind after mulling it over for a while, but at the moment, on the Shockwave scale of 9 to 23 with 23 top, I'd give The DaVinci Code about an 19.