How is this NOT faithful to the book?

Rating: 9/10 (27 September 2015)

That's what reviwers say around IMDb. Let me say it: I started once watching it but got interrupted, I've read half of the book and then saw it all 'till the end.
When I read the book, at least for the part until which I arrived at watching the film for the first time, we have a congruency of the two at 99%. Then, the part until which I arrived at reading in the book (we're talking about 6 hours of reading), so like the second 3rd of the movie, again 99%. When I've finished watching the movie I've read through the next part and found again the same level of congruency. Therefore I think many reviewers here tend to over-react at details, and to judge a movie based off a book without any exception.
But, in films based off movies, when you see eragon, and compare it to, let's say, lord of the rings, you realise there are both good and bad transpositions. This is a case of a good transposition to films, with the important things nailed right, and the mistakes being only some minor details.
One pro is the casting. While maybe for Robert Langdon they might've needed something else, yet Tom Hanks portrays enough well the character. Ian McKellen was a wonderful surprise to find too, he did maybe one of the best performances in the film, together with Paul Bettany as Silas, and Jean Reno as Fache. I feel to highlight these three between the stars that appeared in the film especially. But overall, by reading the book I can say that choices of actors seems perfect.
I want to understand also why people found it boring. because they knew its ending, maybe? Definitely The Da Vinci Code is a fast-paced film, and in the moments of pause it's filled with interesting explanations that keep your attention. Finally, Hans Zimmer's score as usually is very fitting for the entire movie.
What to me is partly a con is the repetitive shoeing of the cilice's bloody wound, a disturbing thing, that wasn't particularly shown this frequently in the book.
Other than this, any cons the movie could have are cons that the book could have.