Let me come right out and say: I was really disappointed in the finale and the whole show. I'm gonna break down my issues point by point in no particular order.
Amon's backstrory: Seriously, that was it? Not only was the connection between him and Tarlokk and Yakone not hinted at, but it all gets dumped on us in a flash back in the second to last episode. And what's with this whole non-sense with Yakone getting plastic surgery, since when did they have that there? And why even do that if he moves so far away anyway.
And they come from a long line of blood benders? The fuck? Hama invented blood bending about 70 years ago, it's simply a very advanced water bending technique which even Katara managed to learn. Just like Toph developed metal bending and taught it to other people. Couldn't they just say that he perfected the technique instead of pulling such bullshit from their asses? The results would have been the same.
The Equalists: So Amon gets outed as a liar, so anything the equalists stood for means nothing now? Non-benders are being oppressed in this society, just because Amon is a fraud does not make it untrue. And these are the most easily swayed people ever. First they all are fine with Amon and his troups taking over the city. Seriously, apart from Asami no one is against this? Do none of these people have friends or family members who are benders?
And then you take away Amon and all of a sudden they just give up, despite the fact that they still have their army and superior machines. All of a sudden it doesn't matter that benders rule the city (the council and the police force) and use their bending against non-benders whenever they feel like it. So they all just liked Amon so much that they all just decided to follow him? Bullshit.
Hiroshi Sato: First of all, I have to second Bolin, how does Hiroshi keep making all these machines? Does he just have a bunch of hidden factories? Where do the equalists get the supplies to make all these things?
Making Hiroshi simply evil and kind of crazy really cheapens the showdown between him and Asami. First he wants to get her to join him and when she refuses he just wants to kill her? The hell? A much better way to handle this would have been if he had tried to kidnap her so he could show her that the equalists are right and to keep her out of the fighting. You don't turn from a loving father into a murderous monster in a few moments.
Korra's air bending and Avatar state: So after completly dropping the ball on the whole "Korra came to Republic City to learn air bending", she simply gets it handed to her. Aang had to work hard to learn all the other elements, but Korra just can do it. And why can she do it? Because Amon is going to take away Mako's bending. So if it's her own bending she is helpless, but for him she can do it all of a sudden? And she doesn't even do anything special with her air bending, it's the same kind of punches she uses for earth and fire bending.
And not only does she get air bending just handed to her, oh no, she also gets the Avatar state and all her other bending back for no reason. So what if she is at a low point, that shouldn't trigger the Avatar state if even mortal danger doesn't do it. Where was the Avatar state when Korra got her bending taken away. And her being able to now energy bend like Aang (who was extremely spiritual when Korra is not) is just more bullshit and a total ass-pull. She has done nothing to deserve that kind of power, she hasn't learned a thing, she is still the same rash and careless person she was before. When she had the plan to force Amon into reveling his bender status, I was like "yay, finally a sensible plan". Instead she just tells everybody that Amon is a blood bender with no way to prove it. How was that supposed to force him into revealing himself, why would the equalists believe her? Because she's the Avatar? Hasn't she learned that this means nothing to these people?
The energy bending also makes anything that happened during the show irrelevant because now nothing has really changed. None of the benders have to evaluate their position in society because they now get their bending back and everything will be just like before. No harm done and no lessons learned. I highly doubt season 2 is even going to address the issue.
Korra/Mako: I've been disliking Mako more and more with each episode since episode 5. The guy is an insensitive, selfish, indecisive douche and he gets away with it. As TV Tropes calls it, Mako is a Karma Houdini. He never apologizes for anything that he did to Asami, heck, he doesn't even break up properly. Oh, you really cared about her? The way you acted the last couple of episodes could have really fooled me, because it totally looked like you acting like a douche to her and never owning up to your mistakes. And in the end he still gets the girl and is shown to be more powerful than Korra since he can shake of the blood bending when she can't and she's the fucking Avatar.
Heck, Korra getting with Mako makes me really think less of her. What's with the flirting, you know he has a girlfriend. And what do they even see in each other, they never showed us why they supposedly love each other. And now we're getting another season with them as a couple? Yeah, no thanks, I think I'm good.
General Iroh: Sorry buddy, but inherited the strategic prowess from you grandfather, not your name's sake. Why was he even there, he should have been much more interesting, but he barely did anything that other characters could have done just as well. And showing Bumi at the end was utterly pointless.
The action: My last point for now. I was extremely underwhelmed by the action in these two episodes. Sure, the action scenes looked fine, but they didn't really stand out from the rest of the series. It just didn't feel epic or special, just like the fights they had before, just on a bigger scale. Heck, Korra just throws Amon out of a window and that's it.
In conclusion, the finale and whole show left me utterly disappointed. The characters were bland and barely developed (especially Bolin and Asami), the plot was either rushed or we wasted time with stuff that didn't matter and the conclusion felt cheap and had nothing but deus ex machinas.
And please don't try to defend this by saying that they only had twelve episodes. That's plenty of time, a lot of animes only get 13 episodes to tell their whole story like Haibane Renmei or Paranoia Agent, who are original series not based on mangas or light novels. Legend of Korra had already an established world behind it, so there is no excuse for how sloppy the writing was.