Melpomene was a pain to beat, since the attacks were mostly composed of many medium bullets with small bullets moving in-between. Thankfully, the boss doesn't seem to do the side-to-side attack a lot.
I tried thinking of possible improvements for this game, I could only come up with two things.
Some kind of nonstopping laser beam (it would require charging time so it's not OP'd) and a sandbox mode, to test out weapons.