So many things going on at the same time!
First and foremost: The end of Legend of Korra season 2. Although the animation was exceptional, there are a few things I am somewhat disappointed about (if that is allowed).
-Korra losing her connection with her past lives :(
Very bad. The ATLA universe would not be the same without the past avatars. I wouldn't go as far to say all their work has been undone, but I hope Bryke will 'repair the damage.' (They probably will, since ATLA had a stellar, if not near-perfect ending even after the heroes' loss at the end of book 2.)
-Keeping the spirit portals open
I think it would be interesting for a time to have spirits and humans coexisting, but there would be too much potential for conflict. In the physical and spiritual worlds, spirits might be angry at humans for disrespecting nature and their homes, respectfully. In addition, Korra cannot possibly keep track of all spirits and resolve every conflict.
Somewhat belated and shadowed by LOK, but still really important in terms of the ATLA universe: the fate of Ursa. I think it is good that she is still alive (more on her actions some other time), but this leaves another loose end. Azula has ran away and most likely will never go back to jail.
Well, this is my first blog post. Looking forward to next year: The Rift coming out in the spring and Season 3 LOK in the fall.