Well I for one have no problem with the changes. Arwens' role really needed to be beefed up (other than the 10 pages in the appendex of ROTK) and Tolkien admitted that at one time. Her and Aragorn's relationship mirrors Beren and Luthien's in the Sil.
In the books even though she's really not in FOTR or TTT, she sort of comes out of nowhere in ROTK and marries Aragorn. If they did this in the movie without any previous Arwen/Aragorn interaction, then the audience has no emotional investment in Aragorn's wedding. It just becomes a cold plot point to check off the list.
As for Faramir, in the book he's pretty much a perfect,noble character who displays little to no doubts. Most of his scenes in the book are comprised of talking talking talking talking. Need some dramatic tension in there. He eventualy does the right thing and is not far off the mark as far as comparisions to the Faramier in the book is concerned. He's just got a slightly longer character arc in TTT.
Besides, in the movies, they're playing up the seductive lure of the Ring even more than the book does (to give it a stronger on-screen presence which would otherwise be lost). So scenes are skewed that way. The ring even attempted to seduce Aragorn at the end of the last movie. It would odd to have Faramir pull a Bombadil and essentially chuckle and blow off the whole thing.
I am such a Tolkien geek