I finally saw Avatar last night. In short, I thoroughly enjoyed it...with a few minor caveats.
First, the story was pretty unoriginal, being little more than Dances With Wolves, Pocahontas, The Last Samurai, et cetera repackaged with aliens. Nevertheless, I don't mind familiar stories if they're told well, and I feel this one was told well. James Cameron made a good choice devoting so much time (almost 2 hours) developing the Na'vi culture, and making it something I cared about as a viewer. Once the inevitable conflict with the human colonists began, I was fully engaged in the story and cared very much about the outcome. Plus, it made the final triumph that much more satisfying. It's something any good story should do. Sure, it was nothing new and totally predictable. But with proper development, it doesn't matter.
Then there were the visuals. Simply incredible. I've often read and agree that science fiction isn't about character development or even plot...it's about the setting. It's about transporting people to new worlds and making them consider the possibilities. In this regard, Avatar was a smashing success in my book. Though the characters were mostly one dimension and the plot was nothing new, Pandora was an incredible world filled with wonder and possibility. Just the kind of thing I want to see in science fiction. Plus, I love movies with cool creatures, and Avatar was chock full of incredibly well imagined and awesome-looking lifeforms.
For one last quibble, I'm really disappointed the Na'vi were humanoids. I understand why from a story-teller's viewpoint. Make them too alien, and human audiences wouldn't connect, thereby destroying the story's impact. However, the Na'vi share no characteristics with the surrounding wildlife. They weren't hexapods, they didn't have four eyes, and they had hair. It seems they would share more features with their fellow creatures if they were actually native to Pandora (maybe they aren't...food for thought).
Also, I found the Eywa concept cool, in that all the lifeforms on the planet are linked together, creating a sort of planetary sentience and consciousness. It might seem far fetched, but it's similar to the Gaia hypothesis, which has been around for a while. Though I doubt there's anything like it on Earth, you never know what might be out there amongst the stars, waiting to be discovered. Maybe there's nothing exactly like what was imagined in Avatar, but there could be planet-wide neural networks out there, formed by lifeforms we can't imagine, creating intelligences with perceptions we can't begin to fathom. See? That's what good science fiction should do.