Under rating threshold (hideshow)
Would be nice if you had something like levels, shop, achievements, upgrades, score, etc, anything that would give the feel of a progression system. Powerups help a little, but not enough.
Also some more info on screen could be added, like how much of the level have you done, boss health could be shown.
Game starts slow, but it gets to a nice pace after you find all the enemy types, unfortunately the game is to short to have time to enjoy it.
And after you beat the boss, your only option is to kill your self.