I really like this idea. This feels a lot like a prototype more than a completed game to me, but that's okay. I think this has a lot of potential to be really fun. Some minor complaints:
* My framerate was horrible in fullscreen mode, it was fine the second I left fullscreen. I like to play games fullscreen, as I get distracted by other applications easily when I can't. But it was very hard to aim with the low FPS in fullscreen.
* It was slightly less hard, but still hard to aim when I had better FPS in non-fullscreen. This is entirely personal preference and came down entirely to the sensitivity in which I can move the reticle to aim. If I don't have a slider to adjust the sensitivity to my liking, I'm almost always going to struggle. Plus there's never really a perfect sensitivity for first person shooters since everyone likes it to be different.
* The UI didn't really pop for me. I know it listed the number of shots I had left still. I'm not sure if it's the placement, the font size, the font itself, but something made it just feel weird to me. It was hard to watch that and what was happening on the screen at the same time.
* It was really hard to figure out when enemies were coming up behind me to attack me. That's okay if there was some indicator for it, but I didn't see / hear it if there was one.
I really like this idea a lot and I think it could be a lot more fun with some polishing and quality of life tweaks. Better visual communication, UI, and FPS would make it really fun for me. That being said, you made a game in 48 hours. That's a hard thing to do. You should be very proud :)