"Glitch is a web-based massively-multiplayer game which takes place inside the minds of eleven peculiarly imaginative Giants. You choose how to grow and shape the world: building and developing, learning new skills, collaborating or competing with everyone else in one enormous, ever-changing, persistent world."
edit: that said, I haven't for quite a while, and it was only briefly. But I was mostly lost and wandering, where Maple Story had quests up the wazoo to keep me focused. Was that part of the appeal, or a transient attribute?
Here's their original trailer, which made me fall in love with the idea: http://www.youtube.com/watch?v=b6O5QXj6n18 Alas, it turns out falling in love with the idea of the game wasn't the same as falling in love with actually playing the game. It still makes me sad to hear they didn't figure out what was missing from making the game really engaging.
