To me, this show can be summed up as "Amazing ideas, poorly executed". So many major arcs were either dismissed or created with a single throwaway line, you could miss an entire plot thread with a single ill-timed bathroom break.
Set up pro-bending story arc with team rivalries, can Korra resist cheating by using other elements/avatar state? >Drop plotline and speak of it again maybe once.
Team forced to live with hobos and maybe confront class and bender/nonbender inequality. Maybe these equalists have some legitimate complaints? >No, they were just being controlled by an evil bender guy who has spirit bending (how did he get this? We will never know)
Last airbender: the fire nation cleverly disarms earthbenders by putting them on sea platforms or in wooden cages. >Korra: "You can't bend those cuffs, they're platinum!"
Regularly mention the question of Lin & Suyin's father. after 4 seasons, finally get Toph to talk about it. >Oh, he was a random guy you've never met and never will. >Everything involving Suyin