I knew the story well enough that I didn't need to see it again for that. The plot and the main characters aren't that good anyway. I wanted to see the world, the wonderfully imagined ecology, the breathtaking scenery, and above all, the critters. And now, I'm again crying over the heartbreak that that so-perfect world isn't real.
I know that this movie has already made an obscene amount of money, but I can't make myself begrudge James Cameron a dime of it. Even though everyone loves to tear down this movie for its too-familiar plot, its ham-handed message, its cardboard characters, and a few holes in the science and worldbuilding which (though trivial compared to the usual Hollywood movie) are undeniable, I have to say that if you have any visual sense of wonder at all, you owe it to yourself to get out and see it. Don't concentrate on the people (human or Na'vi), and don't try to think critically about the script. These will only distract you from the really good parts. Treat it like the art show at a con.