Procedural generation is an interesting topic to me, as it forgoes traditional level design in favor of a bunch of formulas, rules, and random elements to make varied replayable gameplay.
One of my favorite procgen games is Dwarf Fortress, and how it creates a fully realized world with lore and history, and then places both fortress and adventures as relatively small stories in said world.
Also Deep rock galactic is great in varying its caves, from normal tunnels to massive caverns that you can only traverse using ziplines and platforms
Binding of Isaac: Rebirth is the best game of all time and changes gameplay (via powerups) in random combination that can make a god run or a really shit one. Highly recommend it