I have a lot to say about this one, but I'll just start by saying I think it's a strong entry with a great fun factor! I played to the end and had a really good time with it.
The music is quite good and reinforces the mood well, and it's really cool that you wrote it yourself.
Your game has an underappreciated feature for a game jam: the way you display the controls to the player worked really, really well. I liked that I could read everything at my own pace before the action started, but without the boredom/awkwardness of look at a wall of text on an otherwise-empty screen. I'm filing this insight away for my future games. =)
If you're planning to continue improving the game, I would suggest taking a look at two main areas:
Pacing: The game alternates a lot between intense action and sort of awkward periods where not very much is happening. I even had waves where I'm pretty sure literally no enemies spawned (perhaps due to the Not Worth My Time upgrade?), which was just sort of strange. On a similar note, the confine mechanic feels awesome in the moment you use it, but I would have preferred a lower duration because after a few seconds of watching enemies stand still and shooting bullets that aren't moving yet, I'm sort of like "okay, now what?" That one might just be me, idk. I also just think there could be fewer waves between the bosses, or else more variety between each wave.
Difficulty: I actually found the game a bit easy, but not enough to be a problem as I still felt challenged and had fun. Nevertheless, I think it would help to balance out the difficulty for a more *consistent* "challenging but fair" experience. Make sure there are always enough enemies spawning to keep things interesting even with upgrades that reduce them, and maybe look for creative ways to ensure that there are plenty of bullets on screen even if the player can mow through foes with a high-damage build.
Really cool game though, well done.