Fun concept, I liked the physics with the projectiles, and it makes the game much more interesting compared to other vertical shooters. I also love the upgrading system after each win. My only issue is that the projectiles feel to slow and random at times. Sometimes you win in a few seconds, and other times you win after a minute, there's not much of an in-between.
But, that problem can definitely be fixed with more time spent tweaking variables etc.
Overall, very nice :)