Season 2 finale thoughts in detail, SPOILERS obviously, if you have to wait to see it I wouldn't even be looking in this thread if I were you.
Giant Korra fighting the antichrist worked out way better for this season finale than sudden air bending and energy bending did for the last one. If you're in the minority who thought it was sillier or too over the top, allow me spell it out for you. Light in the Dark would probably work if it was just the culmination of Korra's character development up to this point, but what makes it really genius is how she also needed Tenzin to grow and mature over the season. Korra and Tenzin spent almost the whole season apart, and yet it took both of their separate journeys to get here.
To quote from Charles Dickens Great Expectations
For an hour or more, I remained too stunned to think; and it was not until I began to think, that I began fully to know how wrecked I was, and how the ship in which I had sailed was gone to pieces.
So when her country is falling apart and she can't stop it, and she says "I never wanted a normal childhood. All I ever wanted was to be the avatar," she's not really complaining about how sequestered she was. She's lashing out because "the avatar" of her childhood and "the avatar" of reality aren't meshing, so inside she feels as wrecked as those boats Pip was talking about.
While Korra projects those feelings, Tenzin has them projected onto him by his siblings. He's supposed to be older and wiser, so unlike Korra he doesn't lash out (much), but of course he's feeling effects just as harmful. So when he says "I know I haven't been the best mentor to you, but I realized it's because I've had a lot of spiritual growth to do myself," everything comes full circle.
Just like how Aang's energy bending was the culmination of his character arc, we forgive any deus ex machina because the plot isn't as important as the characters. That's what Book 1 forgot, hell, what a lot of stories these days forget. With this much literary context and in a world of magic and spirituality, the final fight could have been twice as silly and we would have still suspended our disbelief. But how silly was it really? It actually all calls back to the ATLA episode The Crossroads of Destiny. The Guru preached enlightenment by letting go of earthly attachments, and what attachment did Korra have more than her own expectations? When she releases the spirits at the end, something that hadn't been done in ten thousand years, we see that she is now her own avatar, just like when Aang refused to kill even when his past lives told him to do so.
I don't agree that other characters didn't get much focus. That was the major problem with Book 1, but even halfway through Book 2 we saw much needed character development for Mako, Bolin, and Asami. Hell, just in those last four episodes we resolved major character arcs for Bolin and Bumi. I understand why some people would feel that Mako, Asami, and Kya are little left behind at the moment, but that's just a testament to the amazing character development that the others got. It certainly wasn't "all Korra".
If I had one complaint, I'd say it's that Unalaq/Vatu died. I thought in the end he was an amazing villain, and there was so much more they could do with him. Then again, I'm a bit skeptical that he actually is gone. After all, neither Rava or Vatu can truly be destroyed.