Everyone should at least try it once. It's alot of fun.
And in response to the OP..... in head-to-head mode, you basically trade off parts of the song. For instance, your opponent will play a few measures, and then you take a few, and it goes back and forth till the end of the song. And there is a little needle-guage in the middle of the screen that points to whoever is in the lead. And yes, it's only fair if you are both at the same difficulty level. You don't get some kind of bonus points for being on Expert. So if you are on expert and your opponent is on easy, you'll probably get waxed unless you are incredible.