Without a doubt, one of the most gorgeous movies I've ever seen. 3D is recommended, by the way.
Cameron has created a $500 million allegory about the wastefulness of human nature, and if you can overlook that irony, and his racism, sexism, his ham-fisted social messages, and his propaganda, you will actually enjoy this gorgeous movie.
Think "Dances With Wolves" in the 22nd century - on another planet, with aliens, and 3D glasses.
Try to bring some childish wonder to the viewing, and you will be riveted to your seat. As far as ALL MOVIES go, I'd give it 3 stars. As far as Sci-fi movies go, it gets 4.5 stars, I think. The effects are bloody amazing. Enjoy!