I was somewhat skeptical going into this, especially given disappointment with the final Matrix movie in IMAX. However, Avatar was outstanding on a number of levels:
1) Blurring CGI with actors - It is so well done that your mind stops trying to pick out what's real and what's synthetic 2) 3D - Lots of previous attempts have used 3D as a gimmick (i.e. lots of things flying at you). This is the first case where the entire movie is 3D as a medium. 3) Creative visuals - Pandora is breathtaking.
It was the first movie in a long time where I was happy to have paid every penny to see it. A must-see in IMAX.