I would say It was unfortunate that the game didn't provide time to upgrade without being shot at, but then I remembered the theme of this jam XD
Here's what I loved :
The upgrade variety, the little explosion canisters, and the simple style of the game (very well executed).
Here's what I would change :
I think the AI is a bit poor. Since they just move towards the player, you can simply drive in circles continually to avoid conflict. To change this, I would suggest adding obstacles to hide behind, as well as a simple pathfinding script for the enemies.
Good job on the game!