Beat all your enemies on the notes of your music. You can select your own favorite song, choose an mp3 and have fun. The enemies will arrive based on high frequencies, low frequencies yield other enemies, fast music, slow music, volume differences, but I bet you can handle them all. Shoot all the enemies you can and get the highest score. That highscore gives you a good excuse to brag about it to your friends. The longer the combos you make, the more money you will earn.
Use the arrow keys or the W A S D keys to move your gyrocopter. The space bar or K key will toggle the firing. The numbers 1 - 3 have a few special weapons you can use.