Awesome music and an impressively detailed game for the time you had! I love the fact that enemies have navigation (which feels like an unnecessary but nice detail), that the UI pops out of the gun, and the awesome little solar flaps on the gun.
My main critique is that there is a lack of game feel (juicy animation, particle effects and more crunchy SFX in general) and that the game feels a bit too easy, even before upgrades (that should be solved by giving the player a lot less health).
Anyhow, awesome job and I hope you expand on it post-jam.