Wish I could have played with friend, seems like I missed out on exploring much of the cool mechanics on this one. Here's some take aways.
-Sound design was flawless, A+
-Entry room was dope, really liked it and being able to test mechanics before game starts. Again wish i would have had a buddy to try it with
-Assuming you already nerfed the HP of the boss to adjust to single player experience, it took too long to take down boss with default gun. I'd make the sunbeam your default gun, and make an even stronger version or triple shot version as a possible upgrade.
-Some of the power ups were useless, because they all competed for the same slot. I could see no reason to pick up shield or melee since I'd give up my ranged attack. There could probably be some strategising with 2 people but I feel like most people would rather have a ranged attack even then. I liked swapping stuff in and out but if you are going to add more utility items, having a separate slot for main attack and for utility items would solve this issue.
Overall I enjoyed playing your game, fun simple and polished with a seemingly cool take on theme that I unfortunately couldn't experience for myself :(