Just for anyone else who wants to read what went terribly wrong with LoK, in both terms of the overall story arc of the show, and the culmination of the season finale, here are some other people's opinions of what went wrong. You'll see that a lot of people had the same feelings I did: those last few minutes destroyed the possibility this show had of giving us something real. It turned a weakening show into a disaster.
In
this one a fan talks about what was done well, and what went wrong. She also goes into detail about why LoK fails when compared to ATLA, particularly when it comes to character development.
And in
this one a fan talks about the importance of a consequences within the context of a mature show. If you're going to have real stakes, there must be real consequences. This is something that anyone who watches Joss Whedon knows he excels at: you are truly invested in the characters because you truly feel for them, and you know that they are not immortal just because they're on TV/in a movie. LoK abandoned that principal, and the integrity of the show suffered.
There are others, some less well written, others that try to play more to the middle line of "there was some good, some bad, but it's just a cartoon TV show, what more can you expect out of it?" and I think those are just BS. You can always expect the best type of story telling, regardless of the medium it's presented in. A story is a story. Period. Whether that's in a song, a poem, a short, a video game, a cartoon, an anime, a novel, or a movie, the story is what is important. And this story just failed on so many levels.
I feel strongly disappointed. =(