Super cool game!
The death screen is really cool! I like how the enemies are dormant until you fight them, and that the next wave is telegraphed, super neat mechanic. The camera zooming out is also really nice. It allows the player to be aware during the important combat sections and the exploration part of the game becomes more immersive.
One thing is when the normal shot shakes the screen; it makes the screen hard to look at and especially with the low contrast red background. The enemy projectiles are also super hard to see since they're red, with the red BG + camera shakes. And with the high fire rate setting making the screen shake even more.
Some ideas you can use to take this game even further would maybe make the player's appearance change on your upgrade path?