The first series, although speaking about genocide, loss and loneliness, it always did it in a very light hearted way. The enemies was presented to was a solely evil, and the allies were presented to us as solely good, with the exception of Zuko, which was presented to us as confused and in needing of approval from the very start.
This new series now presents to us a world not only more evolved with characters older and more mature it also sinks in a much more deeper and darker morality, where the inexperienced avatar is battling with senses of impotency facing a great danger. Given the previous series, the notion of loosing one's bending abilities is very emotional and scary to use viewers, as bending was presented to us as a beautiful thing and the most supreme form of punishment at the end of the series was taking that away. Now, Equalists ideals are not wrong they're methods are. And everything the Bender society seems to do is just reinforce that. There is this moral line being pushed and pulled by this two sides with Korra being thrown in the middle. This is presented to us very early in the series. And the more we go deeper in this strongly political matter, the more we fail to know who the real bad guys or good guys are. In fact, it culminated in this horrible law where non-benders were incredibly discriminated upon, and the image of that one woman with her children begging for Korra to help them, as she was their Avatar too just made the show so much more mature and dark than it ever was in the first series, for the simple fact that while the Legend of Aang had this dark and mature moments, they were never presented to us this heavily in the very first few episodes.