Good Concept, but...
1. No background music or beat made it not really addictive and difficult.
2. You need a better graphic, or else you will just beat down easily by others music based flash game.
3. The "Broken-Heart Meter" is pretty unfair, you should make a meter like DDR ones, you know what I'm saying?
4. Perhaps a better piano / guitar sound?
5. And ya, more self-create songs will be good. Those song featured are quite childish for me.
Ya, that's my 2 cents of mind. :D