I didn't mind the portrayal of Gimli, even though it did stray into borderline slapstick territory at times (e.g. "Toss me"). The kill count rivalry with Legolas was very cool, and true to the books, as was the overall arc (hate that word!) between them, going from animosity and distrust to genuine friendship. I'm still not convinced they needed to have him as comic relief at all.
Speaking of CGI, there was some really cool stuff that I hadn't seen before in a movie. As well as the obvious ones like Gollum, and the huge battle scenes, I'm thinking of the de-ageing of King Theoden, when Gandalf breaks Saruman's spell. That was something I'd never seen before and I remember thinking "how did they do that??"