The previous section hints at something pretty important, but maybe non-obvious: I assert that MetroidVania is not a genre, it’s a framework - a way of structuring games and most specifically the worlds they take place in.
And
This realization that ‘MetroidVania’ is not a genre helps explain why a game like Batman: Arkham Asylum can be thought of as a MetroidVania where its sequels wouldn’t be, even though almost all aspects of the gameplay are very similar.