Pretty fun!
At first it just looked like a plain top-down shooter but all of the different upgrades that you end up getting make the game a little bit more complex. I also love the balls of not stopping the game to let the player upgrade, it's kinda enjoyable that you don't have much time to think and you just have to go with whatever sounds better asap. My evil designer brain wants to go even further, I think the player should lose an upgrade if they're too slow (but as I said it's extremely evil lol)
I liked it, fun stuff. Keep it up.