I've played it and enjoyed it. I do have a few suggestions I'd like to share, if that's okay.
- For purely cosmetic changes, maybe you could add an option to have enemies leave an explosion of scraps via a particle effect to help add to bursting the infected. I mainly suggest this one because I find myself turning away from infected I finished off if they're away from the horde, expecially blimps. You could also add other cosmetic things such as pallets or texture for our weapons that cost experience, to help add an additional sink for that. Also, when the fire rate is increased for the Sniper and the Thumper, their animations don't reflect that so maybe speeding them up as you upgrade them could help better translate that information.
- On to balance suggestions, I'd say the Sniper is in a very weird spot. When upgraded, it tears through early rounds so easily you can just sit right by the ammo pile and be pretty much invincible, but on the later rounds it becomes next to useless against the horde. I suggest toning down its max fire rate, in exchange for allowing it to pierce multiple enemies. I feel that would make it more satisfying then it currently is and stopping it from invalidating early waves outright. The Thumper, on the other hand, is extremely inconsistent. It feels like its hit registration is RNG, with shots clearly phasing through opponents, or mysteriously hitting an enemy I didn't even point at. This also extends to its self damage, which makes it impossible to tell the safe distance to use. Not only does the explosion animation not showcase the blast radius, but it feels like that radius also fluctuates randomly. Sometimes I shoot someone really close and take no damage, other times I shoot someone a good 6 feet away and lose half my health. Making it both visually and mechanically consistent would make it much more satisfying to use. Finally, the AR is just overpowered. I feel like it would be best split into two different weapons, a harder hitting but slower firing rifle, and a high capacity fast firing Light machine gun. That way, you don't get the best of both worlds in one weapon, and have to pick which you would rather have.
- For some new things, maybe a revolver secondary to act as an alternative for the sawn off, dealing enough damage to two shot eliminate most enemies in exchange for having to reload one dart at a time like the Shotgun. You could also add some purchasable weapon charms, like a shield that halves gas damage, a cat that heals you at the end of every wave, or even a detrimental one that damages you at the end of every wave in exchange for more experience or faster cola build up.
Thank you for reading this, and the game is already very fun as it is.