Solid entry! The graphics are a bit lacking, but I value that you bothered making juicy animations that complement nicely with the popping sound effects.
My main concern with the game is the pacing. Ammunition is too scarce. I found myself running in circles waiting for the AI to drop me some bullets.
The upgrade menu pausing the game is also negatively affecting the pacing. I think your game would work better with a wave system. The player could upgrade between waves.
Overall, great game! I believe the concept is solid, and it's definitely on topic. I enjoyed playing it.
Congratulations on your submission!