I think that style of puzzly level design is known as “metroidvania” nowadays? I don’t know that much about platformers, but maybe Keen is too cheery to be considered one of those?
Either way, yeah I noticed it’s less straight-forward to find the exit than in for example Mario games. The whole keycard thing was later repeated in Wolfenstein and Doom. It’s funny to think that basically Wolfenstein is a 3D Keen, sort of 😀