It's a great movie on its own. The criticism is unfounded.

Rating: 8/10 (23 May 2006)

I've read the book and then watched the movie. The problem with all the flack that has been generated is that it's compared to the book far too closely. One cannot compare the two so strictly because they are two separate mediums. Though the movie is based on the book, it cannot follow it exactly; the movie would loose its interest otherwise. And I'm sure most realize this, but seldom is there a separation of the book and movie when one watches it. I too felt the difficulty of appreciating the movie without criticizing its divergence from the book, but the important thing is that the spirit and general plot IS conserved. And in this case the movie holds to both. If you see the film through as a viewer (and not a reader turn viewer), you'll find that it's a great mystery that keeps you interested throughout. The 2.5hours wasn't even noticeable; it seemed like the normal length.
There are only two things that I found negative about the film. The first was that I felt that the theories put forth lacked a little substantiation. That is, a little more proof/evidence to solidify the ideas, even if it's a work of fiction. Secondly, and this is more personal, I would have liked to have seen the Grail had actually been released, and the truth be known. This applies, obviously, to both the book and the movie. To expand upon the consequences would have been quite interesting in my opinion because it would go straight to the heart of the nature of faith.
The book is great, its attention to detail and all the information provided meshes so well that it seemed impossible that the story/theory were not true. The movie is also great; it has all the elements of a top rate mystery and holds you till the end. The story is compelling, striking and gripping. Remember, the spirit of the book is what's most important when watching the film after reading the book.