I must agree with much that has been said here. I only saw the movie in 2d so far but for the 163 minutes I completely forgot about (almost) everything else. The story is a tried and true plot, but with enough variation for it to remain fresh, and for a wide variety of people to be drawn in to the story.
Some points that I really enjoyed:
When the Na'vi leaders are speaking to Jake for the first time I like how they comment on the other scientist avatars as having "their cups already full" and how that makes them harder to teach. I think this is a different, but also very true take on how scientist, though seemingly willing to learn, sometimes are too concerned with what THEY think is important.
The emotion I felt for Jake (and it seemed to be echoed throughout the theater) the first time he returned to his own body from his avatar was so palatable, the disappointment of him returning from a world where he could walk again filled the theater.
Even though they were barely explained in the movie, the variation of the different Na'vi tribes was subtle, but very evident (and the plains Na'vi got screwed in the final battle since it seemed all the ground fighters were completely wiped out).
It's just a small thing, but those little lizards that have the propeller like back spine that glows when it's unfurled was just something that made me smile during the movie.
There was so much more to it that I can't even begin to explain why and how wonderful it was but for all those who have seen it, you understand I'm sure.