I just keep waiting for Elrond to go into end a sentence with "Mister Anderson."
One thing that really bugged me about the LOTR movies was that there were no farm fields around the cities. Okay, Helm'* Deep was a fortress retreat, but the other cities would certainly require a lot of nearby farmland to support populations of that size.
Another is leaving out the encounter with the Barrow Wights from "Fellowship". That was an important part of Frodo'* character development, and shows how the ring has already started to take hold of him. To be fair, to get to the Barrow Wights, you'd have to do EVERYTHING before that segment, and that means letting Tom Bombadil into the movie, and frankly that whole thing was just weird.
"I have a hammer! I can put things together! I can knock things apart! I can alter my environment at will and make an incredible din all the while! Ah, it'* great to be male!"