They made Faramir a much weaker character. In the book, he was the one that said "If I saw the ring lying by the side of the road, I wouldn't pick it up", IIRC. He was a nice opposite to Boromir who was consumed by his lust for power to save Gondor. In the films, Faramir was also almost consumed by it, but for the reason of gaining his father's approval. That's why he took them on that strange diversion to Osgiliath that doesn't happen in the book. He was more concerned with personal glory to show to Denethor than the fate of Middle Earth. It was a nice enough little character arc, and it was pretty necessary to have something more for Sam and Frodo to do to balance the movie out, but it turned Faramir from a wonderfully selfless character, who was a perfect match for Eowyn later on, into a much weaker one. And I liked the old Faramir!
Oh, right, you just wanted me to say "He took the Hobbits to Osgiliath when he let them go in the book", didn't you?
