Well done! I was not expecting any submission in this jam to be using so many projectiles so this was a pleasant surprise. The difficulty progression was also a nice touch.
It looks like you have prepared other sprites for the explosions, btw. It might have been nice if they had been used (ie. there's some variety in the explosions)
On game over, if there are any white aliens left on screen, there's a chance the text becomes unreadable. Also, the life indicator on the upper right seems to be clipped.
Hope to see you in future game jams ^_^