The original Metroid and Castlevania both turn 40 years old this fall. As the two series most responsible for creating the "metroidvania," we're taking this occasion to take a comprehensive view of the popular genre. Samus steps into a room she has seen before. Metroid Prime 4 based its exploration around a new motorbike vehicle The Prime 4 development team considered an open-world Metroid, too, but quickly encountered a problem: Metroid's progression depends on gaining abilities that expand where Samus can go, which doesn't naturally mesh with a world where players can roam freely from the beginning.
Источник
GameSpot