If you're a fan of the Avatar series (which is experiencing a cool fandom renaissance thanks to both shows now being on Netflix) I recommend the two prequel novels
Rise of Kyoshi and
Shadow of Kyoshi which came out summer 2019 and summer 2020 respectively. I made
GatoDelFuego read it and even he likes it (and that guy usually hates everything good).
The main premise is that the wrong Avatar was chosen, which is a bold conceit since we obviously know Kyoshi will be the true Avatar. I expected this to be just the beginning of the story and maybe just played for humorous effect when Kyoshi exposes the poser. But we get a lot of time to care for and like the "fake Avatar" and the status quo, and the implications of everyone's world being flipped upside down by the reveal has such a ripple effect that it really stays the main driving force of both novels. It's very much a journey-over-destination story, which is key to making a prequel stay engaging. There were a lot of times reading this that I thought "that is a bad plot point, I can't believe it's going to go this way" only for that to end being being repurposed as set-up to the real plot point. It stays relatively unpredictable.
It expands a lot on the lore of the world in ways that seem very...natural, for lack of a better word. It's a prequel, so it can't introduce new forms of bending or technology anything that doesn't exist in the shows, but it does explain a lot of things that had to exist, but were never elaborated on. In
The Last Airbender we see how the Air Nomads discover who the Avatar is, but here, we get to see what methods the other nations use. We also get to see a world where the Air Nomads are all still around and the Fire Nation is not the bad guys, and how all of the other nations see each other's cultures and try to keep balance. It explains things that don't necessarily need explaining but are nice anyway, like why Kyoshi wears the makeup, why she uses fans as a weapon, and how she managed to live so long.
Women in the North Pole still aren't allowed to learn to waterbending to fight at this point, and I think the story handles the whole "modern values vs. accurate period piece" (even if it is a fictional universe) incongruity well. This is about 300-400 years before
The Last Airbender, and I liked that they didn't suggest that tradition was a relatively newer one. There's one waterbender who is considered to be just the best doctor in the world and the most we get on it is "any idiot can hit someone with water, the real skill is healing." They never attempt to make her into a fighter or suggest she needs to be. The women from the South Pole can still use waterbending to fight anyway (they're still around, since the Fire Nation didn't go to war and capture them all yet!), so it's not
as much of a restriction on the storytelling.
Just personally, what I like the most is that it salvages the "worst Avatar episode" (I never disliked it personally), The Great Divide. In that episode, it's claimed the Gan Jin and Zhang tribes hate each other because of an incident that happened 100 years before TLA. Three versions of the story are told; we know Aang's is a lie, but we don't know which, if any, of the other two is true. A lot of people hate that episode because Aang lies to resolve a conflict and that was seen as somewhat out of character.
Here, centuries before that incident supposedly occurred, it's shown the Gan Jins and the Zhangs already hate each other. So it becomes a lot easier to believe that NEITHER of the stories are true and it was just some shit that they made up to justify a petty conflict that was just always there. That every few generations some story just pops up to explain why they've always hated each other. That seemed really realistic to me.
On a final note, the story gets to be a little bit more mature since it's not a kid's TV show. A lot of kids grew up wondering why benders never used certain moves that would be instant-kill attacks; we did get a little of that in Legend of Korra, like airbending the air out of someone's lungs, but a lot more of those are finally shown here. Things like stabbing people with spikes made of rock or ice, shooting small rocks like bullets, freezing someone's lungs, etc. Sex is implied but not depicted, and illegitimate children and mistresses become a major plot point in book 2. It never tries to be edgy with the mature content, everything serves the storytelling. It doesn't reach the level of Game of Thrones or anything; the closest equivalent I would say is something like a Star Wars or Bionicle.
Anyway, I highly recommend if you are a fan of this franchise. It's a good story and it fleshes out its world a lot.