I love this idea, truly unique and the art style has great readability. Also liked being able to choose the spawn point for the enemies as it's an extra layer of strat.
If i was nitpicking the player collision can be hard to predict when your shooting gaps, and the music can get a tad repetitive, but can sympathise since Bosca Ceoil (guessing was used) can limit you to making looping tracks under time constraint.
With a few more levels this could make a good mobile game. Had fun, awesome entry!