This show is a slow creep. It's a new time and a new world, at first it's just captivating and fun. The focus is almost on learning the new world and Korra's personality. With perfect punches of nostalgia incase you can't get into it.
LOK is it's own entity, but the story aang and his friends is like the base all the ways they shapped the world led to the changes happening now. Legend of Korra has all the almost all joy and humor of ATLA. But you have to invest in the show at first.
It quickly makes it clear it's a different, much more adult kind of show. It's sweet, funny heartfelt. And then It tackles issues like fanatical extremists, manipulation by toxic family, and worse all building into a core message of the cost of living through and surviving traumatic events. It does it all without blinking or making light of it.
You're gonna be laugh sometimes and suddenly end up crying once in a while. But it's a healthy kind of cry.