A pretty well done entry! It’s nice to see an FPS for a change. ;)
Both the art style and the sound design are nice, the animations and particle effects look good. One thing I didn’t care for were the particle effects on player projectiles. Given that we can’t stop firing, they’re constantly visible on the screen and they make it difficult to notice where the enemy is firing from.
As for the upgrade system, I think it is a great idea, but it would be executed better if the upgrades themselves were things that change the way the weapon works instead of just some stat upgrades. I guess the best upgrade I got was the one that gives you a percentage chance of launching a grenade instead of a standard projectile. Having your weapon constantly change to a different type and having to adapt to that would be really nice. I also didn’t really like the accuracy drop upgrade. In one playthrough I’ve started the game with two of these in a row and hitting something was next to impossible.
What worked really well was the enemy difficulty scaling. Not only slowly increasing the amount of enemies, but also introducing new enemies with different weapon types got the game a pretty good progression. It could easily give the game another avenue to improve, by adding more enemies with differently working AI systems (like enemies that only have a melee attack, so they try to move around the boxes and attack you from the sides / behind).
Overall, it’s a really great take on the jam theme, and a pretty good execution as well. I’ve enjoyed playing it. ;)