We had this idea too! Giving player abilitiy to choose how hard the game becomes instead of making the play itself stronger is a really nice and unique mechanics, and I like how you approach the implemntation with reverse shooting. Music and everything else works great too :)
But what dissatisfies a little is that you cannot win the game. Maybe spliting the game by levels which can be passed easier if the right abilities were chosen and increasing number of available abilities would add more fun to this game, then you could actually win the game, and not just getting the score stats updated?
