I might be of small minority, but I thought that the last season of LoK was the best one. Not by huge margin thou. I loved the way the table was turned. Its easy to be hero, when you have single goal in mind (like TLA was against Fire Nation) but what then? People get bored of hero, when there is no enemy, and start to blame hero for not doing this and that, when everyday life turns against them.
I would love to see Korra team up with the Red Lotus, and actually bring change to the world. Maybe not too radical change, as the Red Lotus wants, but something earth shaking anyway.