The enemies shoot with a frequency so high that you can barely stay in front of them to shoot back. This could be solved by making the enemies move faster horizontally, or by giving them shooting patterns (a bust or the consecutive shots, that a longer delay, for example), or by making you evade the enemies themselves, instead of their bullets (for that, you would need to make them more mobile, and probably with different moving patterns).
Anyway, the art is pretty good. Nice job