Hm, doesn't the fact that I can insert coins without limit make the whole high-score-aspect of the game obsolete?
I played it single-player, it's okay and fun for a few minutes. It falls flat pretty quickly due to the very limited gameplay core. Also, for the most powerups, I have no idea what they do.
I love your clour palette and the music and sound!
Hope this feedback helps you somewhat! :-)