Level design in oldschool FPS formula

A rather major thing about GOOD oldschool FPS - level design. Good oldschool FPS map is a "Place" where things going on. It has distinct areas that are interconnected in a non-linear way even if you can't access all the paths at once. You start off with only part of the "place" being accessible, and at the end you have the whole place accessible by exploring it and finding way to unlock new areas (switches, keys).

It's the same principle of exploration, as in Metroid games / Metroidvanias and it's baffling to me that many people don't see the connection. For me, Doom scratches the same "exploration" itch Metroidvanias do.

OLDER shooters like Wolf and Blake Stone are not places, but mazes where there are no areas that are distinct enough. They are much more deserving of a nickname "Mazeshooter" than Doom which gets called that some times.

Newer shooters take the exploration aspect out of the equation by putting numerous points of no-return, and moving the player from setpiece to setpiece in a linear fashion. Thus, they remove the massive ammount of enjoyement that was to be gained from fruitfully exploring the environment - and that satisfaction from fruitful and meaningful exploration is gone completely.

newDoom is middling in that regard, idiosyncratic even,  some times giving you ability to explore the paths, but also often locking you in and putting no-return points. As if developers didn't really get that part of the oldschool formula