Swimming simulator, perhaps! ;)

It is similar to one, and self-assumedly so by the dev on the Steam discussions. You have some freedom to explore as you will, though not complete - the game ‘gates’ your progress through upgrades a bit more than the usual Metroidvania-fare, so the path you have to take is pretty much given to you.

The game actually saves before most bosses, even if there’s no formal save point.

And when you get really good at it, life pulls out all the stops to make you either own it or get out of the playing field. (Incidentally, this would also contradict the “no ending” part =p )

“The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money.