Changes that you weren't bothered by.

[Boromir88]

This was a rather minor change, but it really added in a lot of "good emotions" into the story, and I enjoy this scene, with Merry and Pippin dancing on the tables.

Theoden being exorcised by Gandalf

I think the way the movie showed it, was obviously not how it was done in the books. However, Tolkien leaves us with a sense that Theoden is a "new" man, hence he's called "Theoden Hal." It may not be to the extent that the movie showed, but when reading certain parts, you get a sense that Theoden even went through a "visual change."