I was thinking perhaps that every beat would spawn a simple to dodge wave of bullets, while the actual beat circles would spawn bullets in different patterns based off of their hit sound. One would be like a firework, one would be a more targeted spray, and so on and so forth. Spinners would be a wave of fast bullets (like the rainbow of bullets that are fired in touhou sometimes) that would take quick movements to dodge. The "Boss" would move to the X value of where the beat circles are located, and you would get points on a fixed rate if you were able to keep shooting the boss as he/she moved along the screen.