What a great game! The gameplay loop is really solid.
At first I thought "Dang, these reload times are super long" but, the more I played, the more I realized this forced you to use different guns. That is genius game design. I enjoyed how I would have to change my playstyle because one of the guns were reloading. Great work there!
I also super loved how the way the enemies behaved made you prioritize which enemies to shoot first. Again, genius game design. I will say, I had no idea the green targets were hurting me for the longest time.
At some point I was thinking, "this is cool, but the upgrades seem pretty repetitive." Yet again, my expectations were blasted by a shotgun when, towards the end of my run, I started getting a larger variety of upgrades.
This game has a ton of potential and I would love to see where you take it, if you end up continuing work on it. It's a great game as it is and I had a ton of fun! I made it to wave 13.