Before you ask; the book, not the movie.
This one has had a fair bit of hype surrounding it, with a lot of people crying "wolf!" I'm going to ignore that to a large degree, and just look at the story.
For those who aren't familiar with the book; go read it. Just straight up, it's a good book. But, essentially, it's a fairly in-depth historical drama, slightly lengthy for some, and again with the romantic subplot. It mainly focusses around a cryptographer (who works with codes, if you don't know the word) and the idea that Mary (Magdalene) had a child with Jesus, and this was the real "Holy Grail" of sorts. Obviously, there's a fair bit of opposition to the idea, and so the "race against time" is thrown in there as well. Oh, and yeah, there's an extremist cult too.
It's certainly not a light read; it's fairly involved, and it has a lot going on with it. But for those who have some sort of interest in history, it's a pretty interesting read, and certainly one of the more classic books of slightly more recent days.
As an aside, many other Dan Brown offerings are also quite good, if you ever come across any of them. I haven't read all of them, but we've got a few, and those I've been pretty happy with.