This was really good! I love the artstyle and the song. Awesome that you can choose from 3 characters, a little strange that their selection quotes are so inspiring considering what kind of game this is. My original plan was to play as all three and switch out when I died, but then I didn't die so I only played as the cowboy hat guy. Only things I can think to improve would be balancing, a couple visual bugs, and an AI bug I encountered.
For balancing, I was able to put all my points into damage and do more than 200 in a single shot by day 3-5, making it so I could one shot all enemies except for octagons, which I could 2 shot. By the time I had 1000 health and a 100 round clip, nothing but the missile triangles could touch me and they couldn't do enough. The health regenerates very slow by that point too, still only +5 every few seconds, so I never made it to full health. The visual bugs are just little things, like the day counter saying day twice and the ammo counter flipping when you look left. The AI bug was with the hexagons, which would all rush to the bottom of the map and stay there. I also couldn't kill them and they'd slow the round count and the enemy spawn rate. Other than that, this game is great! Well done!