White Lotus becoming the world police is shit.
Korra begs Tenzin to train her, stows away, has him bail her out after she trashes the city/resists arrest, and then ignores him.
1920's New York is a garbage aesthetic.
They don't establish the cruelty/domination of benders such that it justifies this huge military response. Benders and non-benders would be family, friends, and lovers, but the show discusses them as if they are distinctly separate groups.
Pro-bending sucks all the fun out of bending.
Love Triangle garbage.
Amon's special snowflake bloodbending is never explained (or how he ignored air bending).
Even if Amon removed the bending from everyone in the city, their children and the children of the non-benders could be benders. It's a fucking Sisyphean task that he could only accomplish if he passed on his blood bending to his children, which is the entire reason he hates bending in the first place.
Amon being a bender doesn't magically invalidate that the non-benders were clearly frustrated enough to resort to insurrection. If anything, being manipulated by a bender is exactly the type of shit they are all mad about in the first place. >S2
Literally too much to list.>S3
It makes no sense that Tenzin would assume that the biggest barrier to becoming in Air Nomad is Air Bending.
Zuko shows up to get his ass kicked then leaves. >S4
Korra keeps leaving Naga behind, for an animal guide she's treated like shit in this series compared to Appa.
Air Nomads becoming the world police is shit and contradicts their entire philosophy.
Korra doesn't try to prevent Suyin from assassinating Kuvira during a ceasefire she negotiated.
It doesn't make sense that Kuvira would hate mixed race Earth citizens, and they try to justify it lamely.