Really interesting game! I will start by saying I couldn't beat any of the bosses, as I encountered an issue where, when I'd shoot, the projectile would go towards the center instead of where I was looking, making the fight very hard as I had to position myself between the boss and the center to actually get a few hits in (I suppose it's not intended behaviour).
The fun factor is there! I couldn't play it multiplayer (as I didn't have friends online) but just bouncing around the arena was pretty nice, I can see it working well in the co-op format! From what I've seen, the boss's attacks are simple but can work.
The highlight of the game is surely the mechanic of "spinning the mousewheel" to reload! I've never seen something like this, and I think that's a very interesting mechanic to have! It keeps you active, and fixes the problem of having to wait a bunch of time before the reload is complete, because this time the reload time increases through skill! Only criticism, maybe the reload is a bit too slow as of now?
The art and sounds are great, and the glowy-cyber feel is very cool.
Nice game! It definitely needs some polish, but I can see it working pretty well once everything is ironed out.