Great comment. To add to this:

> There's something here about the aesthetics of open-ended discovery versus the pleasures of achievement, I think, perhaps in something like a fractal sense.

This is why INSCRYPTION was such a hit. You learn the game rules, and as you figure out the game loop, bam! you get a whole other game layered on top.

A game loop is necessary to create any game that’s not purely narratively based, but the secret sauce is to hide its seams well enough and integrate it with the game world (DARK SOULS and the cycle of death being a whole part of the story, Outer Wilds)

Or go meta and break the player’s expectations like INSCRYPTION did.