Home rules D&D - I was GM for dozens thousands of hours, as it is only limited by my own imagination, so it can be played forever. We were more focusing on story, than on mechanics, thought. Some rogue-lite games I can play forever as well, as they are always different (Dead Cells, Risk of Rain 1 and 2, Binding of Isaac, etc). Unique games like Space Rangers as well. Few MMO I've played for 5000+ hours each, but that was more about collective experience and my responsibility for guild I've made to progress bossfights there (I was like mother to players, heh). It is funny how I dislike interracting with a lot of people, but almost every time I am ending up as a leader, as no one else want to take responsibility on themselves. I will not play those MMO alone. Some exploration and building games like Oxygen Not Included, Minecraft or Factorio I've played a lot and can play even more.