I wrote earlier about Avatar: The Last Airbender and Avatar: Legend of Korra, but that was early into Korra, so I didn't have much experience. Now that the second season of Korra is done, it has disappointed me. It's a fun show, but it lacks what made The Last Airbender special. Airbender was both more lighthearted and more serious than Korra.
One of the most prominent parts of The Last Airbender was the protagonist's ethical and philosophical sureness. He didn't always know the right path, but he mostly knew what he believed. In Korra, on the other hand, it seems like everyone, including the wise elder figures, is an angsty teen, bumbling along in one direction until the story pushes them in another.
They could have done a lot more with the setting, too. Airbender already introduced a fantasy setting with technology. Korra season 1 updated the tech level a bit (though it didn't as much cool stuff with it as Alloy of Law). Korra season 2 didn't do anything more with the main urban fantasy part, and it only touched the edges of the spirit world.
Where Airbender felt unique, Korra feels cliche. Part of the problem is the timeframe. In Airbender, there was one main plot arc spread out over three 22 episode seasons. In Korra, there is one plot arc per 13 episode season, so each story is a fifth as well developed. Another part of the problem is the heavy deus ex elements in the ending. In Airbender, the ending had one deus ex element in the ending, but because the problem and conflict had been so well established, it didn't feel like a problem. In Korra, the finale has multiple deus exes with very little buildup. This is made worse by superficial similarity to Airbender. Remember how the Airbender finale had that "we bent not the elements, but the energy within ourselves" line? Well, Korra has it too! Remember that light versus dark energy bending thing at the end of Airbender? Well, Korra has it too!
I'll probably continue watching the remaining seasons of Korra, but, you know... meh.