It took a time jump, a new female villain, and splitting up our heroes for a big chunk of the season to finally push "The Legend of Korra" over the top, into the category of sequel series that successfully live up to their predecessors. Because of the way it was structured and because of the fundamental differences in storytelling, "Korra" was never going to have the same amount of impact as "Avatar: The Last Airbender." However, it did manage to distinguish itself, develop good characters, and build up to a great finale. Minor spoilers ahead.
With the benefit of hindsight, it's clear that the occasional crossovers between "Airbender" and "Korra" actually hurt the show more than it helped it. The creators were always careful to limit the amount of screen time and involvement that the old favorites like Katara and Zuko had on the story, but they weren't always able to keep them from being a distraction. That was made abundantly clear this season with the return of Toph, who is put into the Old Master role, and at least gets some interesting dynamics to play with when she reconnects with Lin and the Metal Clan. However, as fun as the aged Toph is, and as much as the series teased and hyped her appearances, she's not a big part of this season. In fact, she explicitly declares at one point what the creators should have made clear from the start: saving the world is the new generation's job.
But boy does the "Korra" gang get the job done this time. Tenzin and his family only make brief appearances, and it probably would have been better if they'd sat this round out entirely, since their big arcs were all wrapped up in the third season. The episode devoted to Meelo and Ikki felt like filler. Fortunately, every other character is firing on all cylinders: the Metal Clan from year three, Varrick and Zhuli from year two, new comic relief guy Prince Wu, and of course the villain Kuvira, introduced at the tail end of the previous season. This last book of "Korra" feels like a culmination of everything in the series pushing our heroine toward the self-examination and personal growth that many fans had been clamoring for. It also quietly revisits some of Korra's relationships established in the very first episodes and pushes them in some interesting, daring directions.
I like Korra as a character in this last book far more than I have in the prior ones. Here, she struggles and she fails repeatedly, and she's forced to accept that there's no going back to the way she was - and it's for the better. The show also does a good job of using Bolin and Mako in ways that play to their strengths - Mako is stuck as the straight man to Wu, making him truly sympathetic for once, and Bolin is roped in as a well-meaning henchman to Kuvira, building up the threat she poses. Kuvira is by far the most complicated and interesting villain that "Korra" has featured, and if she'd had more than a season to work with, she'd probably be right up there with Zuko and Iroh. Because she truly believes in what she's doing, she's so confident in her powers, and she manages to build up quite a cult of personality, Kuvira makes a good mirror to Korra. Her campaign of conquest to form the Earth Empire also presents so many opportunities for large scale action and mayhem.
If nothing else, this season of "Korra" has to be commended for the action sequences, which are consistently great. I love that nearly all the major brawlers like Su and Lin are women. I love that they make the effort to give all the characters their own little moments to be awesome. The finale features multiple battles that take place in and around a giant mecha, something I'd always wanted to see done in anime. I don't know what it is about Earth Kingdom stories that lend so well to big, epic battles in this universe, but boy do the creators nail it this time. This season of "Korra," sadly is also notable for production troubles and some truly baffling distribution decisions by Nickelodeon, resulting in a clip show and other compromises, but they deliver when it counts.
There are a lot of little things I can't help wishing for: a better peek at the present day Fire Nation, a better capper for Opal and Bolin, more Asami, and more of the Avatar mythology in general, but I know we're lucky to have gotten as much from "Korra" as we did. The series had its ups and downs, but in the end I can say that I truly enjoyed "The Legend of Korra" on its own and not just as an extension of the original "Avatar." And while I'm sad to see it end, it lived up to its promise and went out on a high note.