Musika can be either be played or simply watched, so it´s pretty much a non-game too. Its spirit feels a little bit like those Llamasoft synths, although I think this one has more rigid rules and goals. Here they are (EDIT 24/11/2008: from apple's website):
"Your music is your game! 'musika' is a ground-breaking music visualizer game for your iPod that uses the songs on your iPod to create original game play.If you see a character that is in the song title, just hit the Center button!Faster reactions will earn you more points!"
It´s good to see interesting alternative games on the iPod. This could be a very interesting platform for, well, any kind of game really. As long as you can play with one button and a wheel (hey, have they ported Rally X already?).