Definitely want to put my thoughts on the finale here, it's partly the reason I'm breaking my CV curfew. Overall I did find Day of the Colossus and The Last Stand to be a solid and enjoyable finale to the show. There was tension in the desperation to stop Kuvira and her army and when Hiroshi died, that was a well executed death scene with plenty of meaning and emotion for Asami. The excellent pacing moved from one sequence to the next deftly with satisfactory timing. I loved the animation style and the wonderful action seqeunces with Team Avatar vs The Giant Mech were so creative and fluid. Plus Korra vs Kuvira was great seeing Korra back in tip top fighting shape.
As for the themes, it's excellent when any show tackles social, political and religious issues in a smart and refreshing way. For The Legend of Korra to do it and still be able to be shown to a younger audience is a testament to the writers of the show. Mature yet accessible content always makes for better shows. So when Korra opened a new spirit portal in the spirit wilds and restored balance between spirits and humans, I guess that took things full circle on her spiritual journey. I do wish more time could have been spent on Kuvira's motives and psyche but there's only so much you can fit in a 20+ minutes per episode so what we got was good. And Mako had an excellent last input to the series, even if his sacrifice would have packed more punch if he'd died in the process. But fitting in Varrick and Zhu Li's wedding plus Mako's funeral in the last 5 minutes would have been difficult I guess.
To make my post even longer now, I almost feel obliged to talk about 'The Thing.' As War Killer and others have mentioned, I would have much preferred the finale to end after her conversation with Tenzin, or even better, if opening that new spirit portal somehow reconnected her with her past lives and she got to talk to Aang one last time. It would have been even better if, by some miracle, they got Aang's child voice actor back one last time to talk about the return of the Airbenders, the spirit portals, the new state of the world, Korra's growth as an Avatar etc. It would have been a wonderful way to compare both series and to pass the torch on from one Avatar to the next expressing his approval and gratitude for what Korra's done.
Instead, we get the rather overshadowing and ambiguous ending of opening the possibility for the Korrasami ship to sail. To be fair, it was at least executed well and its ambiguity works in its favour. It leaves the question up in the air for Korra and Asami to just be close friends or something romantically more. Anything less subtle and Mumsnet along with every Evangelical Christian group in America would be hounding Nickelodeon and the Avatar creators. However, I can't deny that this ending overshadows the finale's own merits. Korrasami was trending like wildfire on Twitter and Tumblr with ecstatic Korrasami shippers over the moon. Perhaps this was one last fanservice as Bryke and Michael have shown interest in shipping before. So what bugs me most about Korrasami is that the finale's most memorable aspect isn't going to be the characters, the thematic undertones or even the fight scenes. It'll be the one last wink to the audience by acknowledging the shipping fanbase and giving them a bi sexual couple hint. And that's a real shame IMO.
I think a big reason ATLA had much more character development and the reason people felt that it answered more questions is because it had about 20 episodes per season. All of LOK seasons felt rushed up until the last episode(except for season 3 and partially 2). The seasons all started off good, but I felt as the episodes went on, they started rushing it. Also, an episode was wasted with Remembrances. A lot could have been filled in that one extra episode.