This review covers the whole trilogy, unlike my last one.
My previous complaint about Aang struggling to kill Zuko still stands. It makes no sense given Aang's past actions, and feels contrived. That's a big problem because "the promise" is supposed to serve as the dramatic engine for the plot.
The other major plot thread, decolonization, starts off strong but quickly becomes sidelined and scattershot in message. By the end, the story seems to say that Zuko was right to defend colonialism (!) as a tide that lifted all boats in the previously under-developed Earth Kingdom. Aang and Katara's points about the racial inequality of the colonies are forgotten after Volume 1. Instead, Katara's POV on Yu Dao becomes a glimpse of her and Aang's future, and Aang himself turns into something of a strawman for total segregation of the Four Nations. Rather than Yu Dao being the complicated political issue it's presented as in Volume 1, with defensible if flawed viewpoints argued by both
Zuko and Aang, by Volume 3 everyone involved in the story seems to come to view Yu Dao as a stand-in for an argument over multiculturalism. It's a jarring shift, and one that comes off as weirdly advocating the White Mans Burden
: the Fire Nation was right
to conquer and colonize the Earth Kingdom, and everything that flowed from that was not only good but the wave of the future. Never mind the extended set-up in Volume 1 that framed the issue along "needs of the many" verses "needs of the one" lines.
The shame is, Yu Dao is actually a neat setting with lots of interesting concepts. There's Fire-citizen earthbenders like Kori, the girls who became Air Acolytes being serious about living out the Air Nomad's philosophy, the colonists who joined the Freedom Fighters in protesting Yu Dao's continued existence, Toph's students, the racist firebender teacher whose school Toph takes over. There's also how some colonists, like Kori, are fiercely loyal Fire Nation citizens despite the colonists being referred to disdainfully by their countrymen in the cartoon. Or how Yu Dao is famous for its steel, and all we see them make are weapons — implying the city is rich because of arms dealing during the war.
The potential for a good story was there, it just either wasn't developed or was lost due to lack of focus. Overall? A lackluster sequel.