Avatar was a great visual experience with the story to back it up. See it in 3D. See it in the theaters, don't wait to rent.
It was a classic 'Dances With Wolves' style story.
The anti-imperialist story line would also have been fine, except that the dialogue took you out of the movie experience. It was too direct of a commentary on the US/Iraq war and the analogy seemed misplaced at times. Regardless of your opinion on such matters it took you away from the story at hand.
The final battle scene was amazing. I actually felt my heart beating fast.