You could say that the animation and fight scenes are what makes this series. You could also say it's the world building and adventure that we have by learning more about the Avatar universe. This show has all of that, but what makes this perfect egg into a tasty omelet is the writing and characters. The characters are so well written and they all have great arcs. Most notably the best one is Zuko's. But of course we get plenty from the other characters too. There are moments that I genuinely cried from how well this show was taken care of especially during the emotional moments. I really commend on how well a show is if it can make us really feel unexpected for a villain. One of the villains is the most hated one, but getting to understand that villain more and then witnessing an emotional breakdown from said villain honestly got me emotional because of how well executed it was. Gosh I just feel so good after watching this show.