Length? I'd personally say that depends on the game and how well they are supported, imo. For instance, I've got ideas floating around in my head that could last a season and no longer. But I've also got ideas that could last 2 seasons to becoming full-fledged games like we usually do. I really think it all depends on the game master and how well they are supported. But I guess that kinda negates the notion of a short-term game.