. Earth and its environmental problems are explored. (Sully has never even seen a forest, so Grace has to practically hold his hand when they go into the woods.)
. We see Josh (Jake) Sully's Avatar being born - Sully actually "births" himself. Also, his reaction to walking again is quite different: it takes him a while to gain any sort of strength, and then he cries.
. It's revealed the Avatar program originally existed to train Na'vi to be an indigenous workforce for the Corporation, since it's so expensive to send human workers. Obviously, they didn't like that.
.There is an Avatar controller who is burnt out because his Avatar died with him in it. He committed Avatar suicide because he had fallen in love with a Na'vi girl who had been killed by the military.
.The Avatars have a Na'vi guide named N'Deh who is sleeping with Grace. Grace survives the soul transfer.