This series consumed my early adolescence. Simply amazing. One of the best cast of characters, some of the best character growth for a kids series, stellar action and animation, and very heartwarming. I was a hardcore Zutarian in those days.
Korra was...disappointing. There was so many great ideas in the various seasons, but aside from the 3rd, they didn't fully realize them. Its cast was also far less balanced and jumbled compared to the original.