The game that I probably go back to the most frequently is Cataclysm: Dark Days Ahead. While it looks like any other roguelike on one level, it has a bunch of different interacting systems, story elements scattered around (if you only find one cataclysm, then you're not looking hard enough), and has a debugging system that (if you're not interested in the action-oriented aspects) can be used to cheat and turn the game into exploring the randomly generated world.