
Platformers that were non-linear and about exploring the gaming area?
Somewhere after the 90s, most platformers became quite linear, you started somewhere and need to find an exit, or fight a boss, then move to the next level. Even those with vast playing areas like Turrican 2 ran that way.
But before that, there were platformers like Jet Set Willy, were you could more or less freely explore the entire game, and choose your own route and way to go, without having to rush to an exit or boss.
Who knows some other games like that?
Let's not include Metroidvanias, even though they fit the bill, they are also their own genre in a way.