The thing about Korra is that the original idea behind her is actually pretty good. After doing Aang, who was a peaceful, serene guy who was averse to conflict and violence, it was interesting to see Bryke go the other direction and give us an Avatar who was brash, hotheaded, and charged into things without thinking. It was also interesting to see her faced with the same basic idea that Aang was faced with, but totally reversed in her case. Both Avatars had to fight an enemy that they couldn't defeat without going outside their comfort zones. Aang, who was averse to conflict, had to fight an enemy that he couldn't destroy without punching. Korra, who loves to punch, has to fight an enemy that she CAN'T punch, and has to handle with more subtlety and delicacy.
These are all great ideas. But LOK never actually does anything with them. They don't go beyond great ideas. Particularly, the thing that makes Korra so shitty as a character is that she really doesn't grow beyond the kind of character she is in the first episode of Book 1. Even in Book 4, even after everything else, Korra is still brash, hotheaded, and prone to solving problems with her fists. Even her talk with Kuvira feels phony and tacked on and not authentic.
And if you consider that LOK was originally meant to ONLY have one season, then the ending of Book 1 is fucking abominable. Korra learns nothing at all, and doesn't change in any meaningful way, and she still gets everything she wants in the end, INCLUDING her man.