ming hua's death was pretty fucking brutal. also lends credence to the idea that no one in avatar intends to murder anyone except for villains, and that mako knew the lethality of it (he only used it against amon and ming hua directly, and to stop equalists from chasing them indirectly). ming hua clearly didn't know the kid could bend lightning, or she wouldn't have gone doc ock on him, attaching herself to multiple kill points. it was also tactically the better idea when he could focus on a really large area instead of trying to make a precision shot in the middle of a fight where he might be electrocuted himself. overall, it's a last resort for him - he doesn't zap ghazan either, when ghazan is clearly beaten and on the ropes.
and i love the part where mako joins with bolin and they start firebending and earthbending together. scene just worked for me.
regarding the conversation about korra - i think i am one of the only people here who doesn't mind her character one bit from season 1 through season 3. she is sheltered and privileged before season 1 begins, which shapes her image of herself as this super awesome badass who is right because she says so. her seclusion from the rest of the world helped make her stubborn and cocky. she was basically home-schooled up through high school and then had to make her way in the world on her own. and she was bright-eyed and optimistic about it, interested in making her mark and doing right. when she's challenged, she doesn't feel like it's deserved at all because she believes, or has been led to believe all this time that she's awesome. when she defeats amon, it happens suddenly. when she has aang energybend her other elements back in, it's a thing she can do because she's awesome and has the ability to talk to past lives (because she's awesome). nevermind tenzin telling her he's proud of her for basically getting a few lucky punches in.
so when season 2 started, it made perfect sense to me that she seemed to revert back to how she was at the start of season 1. i felt it was intentional - korra had learned a little humility after being bloodbent, after having the image of the avatar destroyed by amon (at least in republic city), but when she can just kick ass and save the day? no, it means those people were wrong and she was right (in her mind). it was bias confirmation. the only time she really starts to change is when she discovers she was outright wrong (believing involvement of her dad with unalaq's capture), and apologizes to her parents. and outright betrayal from unalaq actually angers her, but on a more core level, although that's not eating away at her as a person. for korra, it wasn't that she was wrong to trust unalaq, but that unalaq was evil for turning against her. unalaq doesn't do her character development any good from here on out for being a particularly shitty villain who pretty much is straight-up evil and wants to bond with vaatu because of no discernible reason. where amon challenged her ideals, unalaq fed into them, reinforcing the belief that she was good and bad guys were evil.
at the end of season 2, korra starts to change. it's a small gesture with big consequences, but admitting the villain had the right idea and that the original avatar (who she is, kinda) had the wrong idea goes a little into the way of showing that she wasn't thinking in pure terms. she had already calmed down against the people who she was supposed to trust, and after talking with iroh, had started looking at the world a bit differently.
this plays into season 3 where she's still headstrong, still aggressive in some cases, and still believing she's doing the right thing, but she talks a guy down from a ledge. she takes a bad situation (being banished from republic city) and turns it into a positive one (let's rebuild the air nation). during this season, when she's presented with conflict, she doesn't outright resort to aggression. she doesn't try fighting zaheer in the spirit world. she doesn't give a big ol' fuck you to the earth queen (until she's helping the airbenders out). she decides to turn herself in for the good of the air nation. hell, when she's chained up, she rejects aggression because she has to, and is pretty good about it for quite a while. as veelk points out, she doesn't even defeat the bad guy with it. it's the balance in the world she created as an avatar that did. during the final moments of the final episode, she's been truly broken, again, as veelk pointed out, because for once what she thought who she was and what she was good at was not necessary, and now she's not necessary as an avatar. it was something she didn't believe from amon or zaheer, but now she has accepted it as truth (which is my interpretation of the final scene).
it's been a long journey to get korra to this point, but a lot of it made sense to me, and i've enjoyed watching it the whole way. i have things to say about season 2 in general, especially how it doesn't fit into season 1 or 3 very well, but overall i've enjoyed korra's arc and i'm looking forward to how she builds herself back up after being broken down.