It's very rare to come by a good, western-animated show that has so much depth, emotions and darker/more complicated themes to it. The avatar series, and the legend of korra specifically, are absolutely top notch with combining deeper themes and animation. The show's artstyle is stunning with very well thought out battle scenes. The story follows Korra's journey of realizing herself as the avatar, post- 100 year war and Aang's time, where she has to deal with incredibly well written villains, the declining image of the avatar in a more modern world and mental struggles all at once! It's never easy being the avatar, and the writers sure didn't go easy on her and her team.
The main reason why it's so fun watching this show is because it EXPANDS on an already great universe, created in the first series, with Aang. I can never get enough of it! If you consider yourself an avatar fan- GO WATCH IT RIGHT NOW. I can 100% guarantee you won't regret it and have a great time.
