Dan Brown ingeniously combined the "buried treasure" plot with the "secret conspiracy" plot. As a buried treasure movie, it is better than, say, "National Treasure" or "King Solomon's Mines." On the other hand, when they eventually film "The Rule of Four," that has the potential to be a richer thriller.
Conspiracy theories have the advantage of providing an enemy worth fighting, which every good thriller needs, while at the same time explaining why you have never heard of them before. Their fatal flaw, though, is that the more the audience knows about how human history is actually shaped, the less likely they are to believe that there is one organizing intelligence behind it.
Still, some people like conspiracy theories because they bring history down to a scale they can grasp. The Priory of Sion has been exposed as a hoax as thoroughly as the "Protocols of the Elders of Zion" were, but some people still believe in both.
I was surprised at the politically correct twist in this particular conspiracy plot. According to "The Da Vinci Code," the church's conspiracy to suppress the sacred feminine also, somehow, is behind the oppression of people of the "wrong color," or who are just "different." I think the casting of a well-known anti-religious gay activist to articulate this point was not accidental.
So, to give the film its due, the lead actors did a decent job, the plot moved right along, and the settings were glorious. A fine popcorn movie. It is not in any way a serious critique of Christianity or the church.
[SPOILER WARNING: Don't read further if you don't want to know an important bit at the end of the movie.
I thought that Dan Brown missed an opportunity in his choice for the final codeword. "Apple" is cute, in context, but pedestrian. He made a lame effort to tie it back to Eve, but he had not set up the Magdelene/Eve connection sufficiently. I thought the codeword was going to be "Sofia." This would have tied the central woman of the movie together with a sacred feminine image that really does have some currency in the church.
And while we are talking about missed opportunities in holy grail movies, I thought "Indiana Jones and the Last Crusade" would have been much better if Dr. Jones, Sr. (Sean Connery) had remained in the cave as the knight guarding the grail.]