The writers did a tremendous job. It felt a bit special (strange?) to me at the beginning not because Korra, the main character is a heroine, but because she is a person looking and forging her own path. The process is messy, and there is not a clear distinction between good and evil, like in the cartoons and animes I grew up with. This ambiguity probably made the cartoon more interesting as it was slightly harder to guess how things would turn out.
That being said, the story is well written and I quickly became addicted. As I grew attached to the characters, the cartoon dealt with more and more sensitive topics like social inequalities, war, post-traumatic stress disorder and eventually LGBT.
While I do not expect children to read too much between the lines, or one day quote The Legend of Korra in an argument about social inequalities, this cartoon is still for them a first exposure to some of today sensitive topics. Hopefully it will help them open their mind.
It was definitively worth my time. The Bryan Konietzko’s tumblr is also quite interesting to read.