Really fun!
I like the idea about the upgrades, I'm glad I kept playing haha (I hope players will stay until upgrades)
The beginning is tough, it's hard to understand what's moving and what's not at first
I also really liked the fact that you're being punished for staying back, or looking for a safe spot
You're not rewarded for it because it lasts super long and obviously your "safe" spot is only safe because it's guarded by a block, that also prevents your projectiles from hitting the boss
It was really fun having to keep the pace during a run, it took me several tries, but I liked it, once you get it, it feels really cool!
After a few levels, you're getting a bit broken (but not too much), I know it's hard to balance ,but it also feels rewarding to be able to beat everything faster after having invested a bit of time
Maybe on level 3 it's hard to see what's a boss projectile or a shooting enemy since they are both purple
Great audio and visuals overall too, nice game! :D