I was able to catch the Avatar IMAX (lite) 3D screening in San Diego a few weeks ago. I have to say that the experience was breathtaking. The screening lasted about 16-20 minutes with the Avatar trailer in the end. I will also keep this review spoiler free.
There was a brief introduction by James Cameron celebrating Avatar day and it immediately starts off with some sort of RhinoHammerheadDino looking creature. Right away the detail that is put into the forest and surrounding areas are clear and the depth perception in every shot makes you feel like you are watching the film in an actual forest. I was lucky enough to sit right square in the middle of the theater so it may the viewing pretty spectacular. We see Jake , who is in a wheelchair and a soldier, who is preparing to enter his Navi' ( Avatar). What happens next is him travelling to Pandora and interracting with the other inhabitants of the planet. The four scenes included the lab, jake running from the rhinodino , jake at night with Zoe Saldana's character, and another scene with Jake trying to get on a banshee in pandora.
Overall the experience was none other I have witnessed before. I believe the last time I got such a good reaction from a scene was the dinosaurs from Jurassic Park. The special effects were cutting edge and not scene in film before.