The change that offended me most was making Gimli into a buffoon.
I kind of liked Elrond as "young Sam Neill with post-traumatic stress," though. I thought he was a bit bland in the books :-).
I could live with his changes - Elrond, I mean. Though he wasn't NEARLY that grumpy and cynical in the books...
Some of the other elves didn't fare so well, though. Haldir - ugh! I know he's just a minor character, but that bothered me just the same.
And, as Mamzelle said, Aragorn's being so unsure of himself and kinda hiding from his duties irked me, though I've kind of gotten used to it. It bothered me most when I first saw FOTR.