Loved this! I would suggest that you find another way to make firing the bullets visually interesting, as the flashing background is a bit sore on the eyes (especially, I would imagine if you have photosensitive epilepsy).
Trust me, it was WAY worse. My eyes actually hurt during playtesting. Had to do it this way because I knew I wasn't going to be able to add SFX, which would be better feedback (at least I think so) than flashing. I'll have to do my research. Thanks for the comment!