NetHack 3.6.6
It's famous in the roguelike world but I dislike that it is practically pretty much impossible to win without spoilers [0] (which means you have to read about it in wikis and co. to find a strategy that works).[0 I know there are some people who managed to ascend (win) without reading up, but they are probably in the < 0.01% so it's definitely not the norm.