My major problem with the film (SPOILERS)
I'm absolutely poisitive that fellow posters will prove me wrong but I watched the film for the second time today and I'm actually struggling to see what effect the Robert Langdon character has on the plot of the movie. It seems to me that the plans of the villain go off pretty much without a hitch until the very end and its only because another character has discovered the secret and literally hands Langdon the information before dying that the villain is discovered at all.
Yes, he runs all over the city decoding clues and finding the path of illumination but ultimately all he actually does is save the life of one Cardinal, who will admittedly go on to become Pope, but in doing so does puts a hell of a lot of Italian police in mortal danger. He saves one priest, he causes the violent death of about 12 cops.
He's done her. He's done Mrs Lop-sided.