What does your Facebook app do? Does it have a strong viral component? Those almost never are able to direct much traffic back to your site, but they can often do what your site does, possibly better, and spread faster.
This app feels like something I'd just skip by, though maybe the experience would be much better if I were sent a song. But just getting there directly, there isn't much to do. There's one song to play, which is cool, but how do I find more?