Quickly:
Did this feel kind of flat to anyone else, or was it just that my blood sugar was crashing through the floor? I mean, "you won't get away with this" twice in one episode? And almost everything else in the flashback felt very stilted except Sokka (Sokka! ♥). Plus I could see where they had to skip a lot of reasoning and alternative-exploring to get the plot to move sufficiently, like going right to confront Tarrlok on the apparent hope that he would just immediately break down and confess, and that was annoying.
Anyway. Was he working with Amon to be the city's savior and then found that the alliance of opportunity broke down sooner than expected (is that why he had a prison in his basement?), or was he just an opportunist?
Also, I don't think I realized until now that Korra doesn't metalbend. (Aang didn't either, right?)
Lin busting them out of underground, Korra rescuing her own damn self—good things, but still: meh.
Also, you all should read How It's Done by skygiants, which is set about ten years before Korra, because Toph, Katara, Zuko, and Sokka + probending = so much fun.