First, the bad. As many have said, the storyline was pretty much "Pocahontas" meets "Ferngully: The Last Rainforest", and there will be no one under the age of 8 who won't be able to figure out where it's going about an hour into the film. In true Hollywood fashion, corporatists and military people unable to see shades of grey are the bad guys, and enlightened environmentally-conscious multiculturalists are the heroes. The technologically-deficient natives are able to defeat the bad military people by becoming one with their surroundings -- never revealed is how they plan to hold on to their reconquest of their moon if the evil humans decide to use kinetic energy weapons from low orbit.
The good, however, is amazing. It was, visually, the most beautiful movie I've ever seen. It's the first movie where you can say, "They spent $300 million making it, and every dollar is right there on the screen". I'm not sure how good it is in 2D; this is one where it's worth spending the extra to see it in 3D. This is the future of movies -- hopefully with better stories next time.
Overall, I give the movie two out of 5 for the story, and six out of 5 for the technical aspects, resulting in an overall four Politically Correct Reformed Marines Straight Out Of "The Last Samurai" out of five.