This was a neat concept. It was cool starting each level with planning your shot pattern. I liked how each had it's own sound and visual pattern, and I had fun balancing what had the coolest sound with what had the best attack for each level.
It might be helpful if you had some sort of preview of the shot pattern before starting the level. It would allow for playing with different patterns without worrying about the enemies. Having the player bullets and the enemy bullets being different colors would also be nice and make it easier to tell which was which.
The biggest issue I had was there were a few times when either I would hit the last enemy and then get hit with one of their remaining bullets or vise versa and both the retry and the next level screens would pop up together. The retry was above the next level, so clicking the button would have me redo the level. It felt reasonable redoing the level, as I did get hit, but it was a bit disconcerting having both pop up.