The thing I love about this series is how the author wrote so much into the series by being constrained to what the games gave him.
Green's Raticate, for example. The entire theory comes from him using it up to St. Anne, but not afterwards. Gameplay-wise, they wanted to replace it with a stronger Pokémon. But the author here made it the backbone of several character developments.
Same with Karen. Her whole spiel about using the Pokémon you like instead of what's strong in Gold and Silver was just flavor text - in general, she's just an Elite Four battle and nothing more. Combine that with the fact that she uses Dark-type Pokémon and suddenly the author writes her as an activist who tries to stop discrimination against them - it just bends in so perfectly.
For some reason, I love when people have to use others' writing as a springboard to do their own thing. In the comics side of things, Al Ewing is great for taking whatever Marvel stories came out and tying them up in his own little narrative. Grant Morrison too. And this is even better.
I wish people could do the same thing Festival of Champions did, but for other franchises. I know Pokémon is the big one, but there are so many reimaginings that could be great if done well.