If you think the CGI of the machines at the beginning when Jake was arriving at the base was great, then you're very easily impressed. If you didn't think the CG that was used for the masks they were wearing wasn't poor, then I think you need your eyes checked. I'm sorry, but a lot of the CGI was not "great." Jake's avatar didn't look very real when he first took control and was running around, it was not impressive. Much of it looked like it was video out of some high end video games. It was NOT photo realistic.
The 2nd half of the movie, however, was far better, and was far closer to being photo realistic. There is an extreme difference between the quality of the CGI during the earlier part of the movie and and the end of the movie.
To be really impressive would being having the Navi, looking as realistic as they did the 2nd half of the movie, in a real world environment.
Impressive CGI is CGI that you can't tell is CGI, or makes you forget that it's CGI. Avatar doesn't do that, or when it does make you forget, it too often reminds you at some point that it's not real.