You know? I think you've hit on something here. It's true that there doesn't seem to be any escalation or even really urgency, but I get the feeling that wasn't your priority for this jam. You made a solid, well-constructed prototype for an idea you thought might work, and as far as I'm concerned, it did.
I see as well you intended for there to be a "bullet budget" so the player couldn't overspam bullets and trivialize the game, but I wonder if you shouldn't lean into that. Give players a shooter with no ammo restrictions and they'll fall back on the classical ABS method: "Always be shooting." What would be more engaging? Suddenly losing your ability to shoot because too many bullets are on screen? Or using that as a tool to avoid getting overrun? I know for my part I had a good time manipulating the stream of bullets to shoot around corners, and I don't know if that would be as enjoyable otherwise.
Also, if you're willing to share, I wonder what technique you used to curve the bullet paths? It was really consistent, even when I tried to mess it up.