Oooh, it took me a while to figure out the timing system, but once I got it (hum, I mean, once I read more carefully the rules), it was nice!
I didn't know the lyrics at all, but the system is great. I love the presentation, the UI is intuitive while having some personality. That engine alone is pretty cool.
Mixing quiz with timing is a nice idea. Maybe the stamina decreasing is a bit too punitive (especially on my first try where I thought I was losing because of my wrong answers). With a selection of songs (so that players can find some they know), it could work really great!