I am not sure why people are saying that this movie lacked a plot. Even though the movie was almost three hours long, by the time the credits were scrolling, I couldn't believe it was over. As far as the plot, did any one notice what year this movie takes place? 2154! We are the aliens (love that Weaver was in the movie BTW) and the bad guys. Avatar is a perfect representation of the "I want it, so I am going to take it" mentality that is the world we live in today, not caring about who or what stands in our path even if we don't understand the consequences.
Seeing this movie in IMAX 3D is the way to go, the effects and visual presentation was outstanding. I am not sure if I would have enjoyed it as much in a regular theater.