I think it all really depends a lot on your definition of success.
I've heard people talk about how their game is a success because they've had so many people log on every night. There are people who think their game is successful if there is a log posted every night, if there is a plot run every month, if their mom told them they would love to play there.
Man, I said this in a post beforehand but I agree with @Thenomain . Sorry, dude, I promise I'm not trying to stalk you or something. My idea is that a game is a success if people are having fun. If people are scening together without much prompting and scenes and plots are organically starting to link into the game? That's a success as far as I'm concerned.
Basically, if I can log onto a game, like the concept, app a character and start building my way into plots and character development, then that's a good game.