I THINK UNALAQ MIGHT BE A BAD GUY!
So thoughts on the finale, and season as a whole. I still enjoyed it, but because of some seriously plotting issues, and some of the most egregious use of Deus Ex Machina in a series already notorious for it, I'd still probably rank it as the worst season of Avatar as a whole.
The villain was too obvious, the first half was very dull with the civil war story line, the pacing was really really rough all the way through, and while Beginnings is among the best things the show has ever produced, it still couldn't make up for the problems as a whole.
What did I like? Well, with the exception of Unalaq, the new characters were all outstanding, and I'm glad they gave themselves a way to use Varrick, their best new character, again next season. I would have loved more 24/7 Bumi time, but what we got was great. I thought Tenzin's story of struggling to live up to his father's image, and realizing that his father wasn't perfect, was outstanding. The parts in the spirit world were all a lot of fun, and every episode past "Beginnings" was mostly solid.
What didn't work? Unalaq, Unalaq, Unalaq. The guy was an obvious villain from the start, and he never got any more nuanced. I liked the Dark Avatar storyline (even if I felt my take on it could have been better), but otherwise the character was very flat. Like I said, the pacing of the first half was just bad, and the civil war story only got in the way of telling a far more interesting tale later on. Not to mention Korra apparently forgot all the lessons she learned last season, which really bothered me.
So overall it's probably my least favorite of the seasons. I'm still really looking forward to next season, of course, but I hope they've learned some lessons in the mean time.