Wow, this was incredible! I loved the upgrading choices, the UI menu was very intuitive, and the prices seemed very balanced.
I loved the mechanic of the big square disabling one of your sides, that was very clever. The sound effects were very satisfying too, great job on those.
The first I would recommend would be making the enemies have half as much health, but twice as many, because the game felt a little slow at times. The second thing would be to add a music track! I know that it is daunting to create a music track if you haven't done it before, and I 100% get it if you want to challenge yourself to only use stuff you made. I think that music just makes games so much better. Even a simple synth melody with a basic beat goes a long way!
Fantastic job overall :)