I had pretty low expectations going into the film because of all the bad reviews, but I can honestly say I enjoyed the film. It wasn't perfect by any stretch, but it was a decent adaptation and remained faithful to the book. I think the reason why people called the movie boring is because so much of it is all explanations. If you've read the book, the suspense is taken away (which is pretty much what kept the book going) so all you're basically left with are the explanations. It's in no fault of the screenplay adapters or the director. I don't think they could have made it any more interesting or exciting unless they totally reworked the story to make it more "Hollywood". I for one don't want that and am glad they took the faithful route.
As for the acting... I enjoyed Ian McKellen immensely. He made the movie, imo. While I adore Tom Hanks, I don't he was the right person to play Langdon. Throughout the movie, I just saw Tom Hanks on the screen and not Langdon. They should have gotten a relatively unknown actor to play Langdon. I think for all popular fictional characters (eg. Harry Potter), a cast of unknowns is the only way to go. As for Audrey Tautou, I didn't like her so much at the beginning of the movie (the washroom scene was way overacted, same for Hanks in that scene), but she slowly grew on me and won me over by the end of the film. Paul Bettany was great as Silas. I have so much pity for that character. So misguided.
My only complaint is that they didn't explain the Vatican's role enough in the movie. The priest (I forget his name) and him getting those bonds were totally lost on me. It seemed totally detached from the rest of the movie.
All and all, a decent movie. I give it a B.