How do you know when your game is successful? How do you know that you have one of those games where the players are really into the story and action? How do you know that your game isn’t just good, but great?
These are hard questions, to be sure, ones that don’t always have clear-cut answers. Sometimes players won’t tell you if they’re not having fun because they don’t want to hurt your feelings. Sometimes you misread your players and think they’re really into your game when they might not be.
I believe the mark of a successful game is when players give back. Perhaps they want to create something for your setting, such as a new technology for your sci-fi game. Or maybe they want to expand their character’s backstory to fit in better with your game, which in turn gives you new NPCs to use in future games. Maybe they want to build a new fortress or space station.
It’s at this point, when players give back, that you know they are invested in your setting, and you have a successful game.