Nice little game though not very difficult on account of the basic enemy AI. Won without having to loop as when the maximum amount of enemies had spawned, I was able to get them all clumped up and from there could just circle them.
Adding enemies with different patterns would go a long way. Another commenter mentioned Geometry Wars, which would be a good game to take inspiration from.
I encountered a bug where my ghost from a prior loop (when I went back and tried out the looping) started firing out the special 360 attack as if it were its normal shot. Was actually pretty cool, though.
Good work in any case and I wish you luck in expanding upon the game.