The CGI was impressive, and some of it pioneering. But the moive industry was heading in that direction anyway. I was more amazed at the "little things" they did, including the details of building the Shire down to the last detail.
I was especially impressed with work they did with forced perspective. Especially the ability to have a camera move by having part of the set move along with it, so the forced perspective is never lost. The little plates for Gandalf, and the big ones for Frodo, kept the illusion intact.
I was amazed with the "split-level" horse cart for Gandalf and Frodo. Who thinks up things like that, except someone who wants to make the best movie possible?