Yeah I know what you mean. Book 1 was pretty darn plain, but I don't think Mity expected it to blow up like it did, so they kept their aim low. Book 2 was a massive upgrade story wise and in terms of how much content there was in the world. Book 3 took another step beyond that (though I personally didn't care for the actual story in book 3 much). Book 4 just doesn't feel cohesive; it feels like these are a bunch of mini stories centered on Korra, but there's no overarching theme to it all other than "make Korra feel bad". I'm all for humiliation and berating Korra, that part is great, but the actual story; its cohesion and how it's all put into the world seems very lacking compared to the previous two books. It's like we took a step backwards and this could have easily happened between book 1 and 2 in terms of how well it's put together.