Agreed with TigerQuoll about the games with randomly generated maps, or even procedurally generated enemies or encounters.
The idea that you can’t predict exactly how the game will play out makes them replayble. Master of Magic, Transport Tycoon, X-com are all games where the gameplay emerges over time.
Other games i’ve returned to many times seem to be because i’ve forgotten what happens, then you have those nostalgic moments where you go “Oh I Remember This!!!!”, but it’s more like watching a favorite movie again rather than enjoying a new but familiar experience.
