Legend of Korra: It's all about Korra (Final Edit for the Finale, limited spoilers)
There are four ways to look at the series:
1. You can constantly compare it to the original
2. You can enjoy the series as a expansion of the original
3. You can enjoy it for its own merits
4. All the (or any combination) above
I have always been partial to the second, however I think the show is supposed to be looked at through the third. Unlike the previous series which was also about world building and balanced some time with the deuteragonist(s); Korra's story essentially states that "if you aren't relevant to Korra's journey then you don't really matter".
My passive aggressive summary:
Book 1: Aang makes one of his few appearances and gives Korra energybending, her other three elements, and the Avatar state. Because... she earned it by crying?
Book 2: Events from Book 1 (the equalist movement) were handled off screen. Korra transforms into a giant spirit being because, according to Tenzin, Korra's spirit is super powerful regardless of Raava (or the "Have you seen these?" past lives). No reason given, just accept that Korra is TEH AWESOMEST EVUR!!!1!!!11! (or fanwank something).
Book 3: Screw the new Air-benders, or how other nations are handling Harmonic convergence, Korra feels sad because of her failures.
Book 4: Address Book 3's circumstances (the Red Lotus and the infrastructure of republic city) off screen. Ignore everything that's happened or any other character, Korra has a "special" friend. Oh and there was a ceremony or something too.
Personally, I don't think Korra herself was particularly interesting (though she had/has a lot of potential). Mostly because I think they played her too safe when distinguishing her from Aang. Korra still ended up being a level-headed, spiritually strong Avatar. So what's the difference? Korra is a special-snow flake, end of story.
Overall, the finale was disappointing; which, for me, ruined the rest of the series.