Spelunky is, I think, better designed than any other roguelike, platformer, or roguelike platformer. It’s not because it’s a work of genre revivalism. It’s not the procedural generation, which jumbles level geometry upon every funny, frequent, fist-shaking demise.
It’s the bats. The bat, found in its opening world, is a dimly flapping lense through which the entire game can be better appreciated.