Some thoughts.
1) Side-scrolling bullet hells aren't very commonly seen around here, so it's nice to see one coming from you.
2) Why are there no mouse controls? A lot of us who have handled vertical bullet hells have found it far easier to handle it with the mouse because of the hitbox, it's easier to do precision navigating through fields of bullets with the mouse.
3) It works fine for what you've given.
4) Depends on what graphic style you want to shoot for. Are you going for a Touhou-ish style, something from Epic Battle Fantasy, or a Western cartoon style? Or are you going for something completely quirky? You've only given us the enemy without backgrounds or even a glimpse of what the player character looks like, so we can't say much for now. If you have any concept art whatsoever, put a screen or two up!