This film was probably the most amazing cinematic experience I've ever had -- a completely wonderful time. The graphics are amazing, the sound was right on, and the battle scenes are great. The story is kind of old, yes humans are destroying the world and there are allegories to the conquest of the Americas and Africa and even modern counter-terrorism, but I still very much enjoyed the film.
The IMAX experience was fine but I don't know if it would be that much better than regular 3D. The theater we saw the film at had some technical issues which caused the film to stop in the last battle, and it took them about 10 minutes to fix it... so that kind of sucked, but the film was still great.