Lots of character development the past two episodes! "Original Airbenders" is probably the first Korra episode to feel like an episode of A:TLA (in a good way). It was genuinely funny, filled with a crapload of world-building on behalf of the air nomads. I think that episode gave us a better insight into their culture than the first series ever did.
Lin's backstory with her sister was great to see, though I still think there's more to it than we were let on. It seems the theory with her issues with her sister and Tenzin might be that she's infertile. She doesn't have children, she might even hate her sister for having this large, loving family. That would also explain her anger towards Opal. I mean, Tenzin needed more airbenders... and Lin couldn't provide that. Even if this is never said outright, this is pretty much what I'm going to believe unless we are shown otherwise.