Power up feels super good, so that's good !
However you really need something that makes the game restart.
Also the difficulty curve is not really subtile, because at the first second there's already 100 kind of enemies in front of you so it's super difficult. Maybe you should introduce some enemies one by one, or two by two before making them interract all together
Oh, and, one life until gameover is a bit mean. Maybe think of a life system with instant respawn or something?
:)