Yo, good stuff. I adore the aim & shoot main gameplay loop - it's fun and feels good. Some of the guns took a lot of reload time which caused me to switch weapons, eventually using up my full arsenal to defeat the boss in a timely manner. This was a lot of fun, but it also felt iffy in the sense of "is this intended?" I think one way to solve that is to add some reload sound effects, or maybe a sound effect that plays if you try to shoot while still reloading. I did notice that the mouse pointer changes though, so that was a nice touch.
Ultimately, I had a lot of fun, and I really wish you had time to include more bosses! I actually enjoyed the fight a ton, it was really cool to look at and got me excited. It was just a little short for me and I really was hoping that when I knocked down that guy's HP, there would be another boss waiting for me. :)
Excellent work!