What would you have changed from the movies as they were?
I mean, I can’t think of that many deviations from the books off-the-top-of-my-head. Tom Bombadil got cut, but he had a very different flavor from most of the rest of the series. Legolas “shield surfing” was an addition to the movies and was kind of obnoxious, IMHO, but it wasn’t that much of an ongoing thing. There were some changes around Aragorn going through the Paths of the Dead, but nothing there really bugged me.
EDIT: I’m pretty sure that nothing in the books said that the charge of the reinforcements at Helm’s Deep was down that steep of a slope – that’s probably just not practical.