Here are some of my expectations
Personally I woud LOVE to see an airbender (most likely Jinora) in pro-bending, even if it was only for one match.
I really hope that most of the characters in book 1 play a large role in book 2 (aside from amon and tarrlok) as appossed to getting rid of the airbender kids, Iroh 2, lin, and even tenzin.
LOTS (and LOTS) of flash backs from various time frames, from when aang was only like 20 or 25, or when aang was like 40-45 and tenzin was 10-15
Korra using airbending
Korra getting some enlightenment on her spiritual side