Understanding the concept and upgrades is a bit confusing at first, but once I figured out that the portals were intended to have both upsides and downsides I was able to get the idea. I quickly discovered that the red portal upgrades were very abusable, especially the size down one that ends up killing enemies instantly if you upgrade it enough. I ended up focusing more on guiding the enemies into red portals and mostly ignoring my gun and the green portals, because it just felt like the most optimal strategy.
Balancing issues aside (I know it's really tricky in a game jam, I had the same problem) the gameplay loop did make me want to keep playing. I got pulled into wanting to see what the next upgrade could be, and it was super satisfying to watch tons of them get wiped out at once by portals.
Overall a creative idea with a good gameplay loop that just needs to be tuned a bit :)