Feels pretty neat and the upgrading system is a great touch with the positive-negative dilemma to choose from. Simple but nice!
The good:
Great feel, simple gameplay. There might be a bit too much camera shake but the gameplay does go pretty well. Playing in a constrained arena is the simplest implementation of the theme and it's OK at best. But the gameplay makes up for it.
Very approachable difficulty and the upgrading system helps make up for lack of skill.
To improve:
There is a distinct jank with how the sprites move, and there are other things that could do without. It's hard to tell whats the actual hitbox of the player with how big the player sprite is and while I played the game relatively fine, I also felt confused occasionally when I took damage.
There could be additional mechanics at play.
Otherwise, simple and good!