1st Season: Shit kid Avatar and a good villain. Decent season, althought mostly fueled by hype/nostalgia. Cracks and flaws were mostly ignored.
2nd Season: Still a shit kid. Villain is boring but spirit world adventures were decent enough. Also: UNCLE IROH MUFUCKERS! LOOK AT DAT O.G. SIPPIN ON DAT TEA N SHIT!
3rd season: Our protags are all bumbling fucks or dumb fucks, even most of the adults. Tenzin and Milf Beifong being (not so consistent) exceptions. Zaheer and company are the coolest and have the biggest dicks and are OP as fuck. The show has now patently proven that it has terrible writing. One would be blind to not notice at this point.
4th Season: Whatsherface just being best girl(that cold, sexy, calculating, merciless bitch. Take my seed and let us raise our little ubermenschen in our prosperous earth kingdom) but also being too radical about it. Writers finally reach "Fuck It" threshold and insert a mix of their feces and piss onto their pens to serve as "ink": Double down on muh feelings, muh akward relationships, muh traumas, muh super badass but vulnerable avatar womyn. At least we got a giant robot, but even that was shit-tier.
BONUS: OMG SHE'S A SURPRISE-LESBO! THIS IS CANON BUT WAS IN NO WAY PLANNED! SEE FEMINISTS AND HOMOS? WE'RE THE GOOD GUYS WE ON YOUR SIDE!