It took me a longer time to accept the change on the stairs of Cirith Ungol. Although it made sense that there should be some drama other than just Frodo and co climbing stairs they might have taken another part from that chapter and used it instead.
Also the warg attack is slightly awry and they never had a good explanation for that one. However, when I heard in the documentaries that they had had the idea of letting the wargs attack Edoras
I was glad that that never happened.