Fin game with really nice art, but i'd maybe suggest balancing enemies HP, because 3 hits can be a bit too much with the amount of enemies that currently spawn. Finding a balance where if in example you don't miss a single shot gives you enough time to not suffer HP loss could be a neat addition for the first level.
Also, having an off-screen indicator of where the enemies are coming from could help as well for positioning yourself, since the camera only covers about 1/4th of the whole field.
Cheers ;)