Earning money from something is nice, it keeps the wolves from the door. But I prefer to view success as getting something more permanent into the world, that might be an artwork that is shared, or an idea that inspires others toward their own projects.
So, Thanks to Josh Mannon over on G+ I can definitely consider Ghost City Raiders to be a success.
He's developing the core of a dungeon delving game that has been inspired in part by the work I've done on GCR. With a bit more work it looks like it'll shape up to be a fun little game.