This was really satisfying and fun to play. Especially at the beginning of a level I was standing in the center of the level, watching the black circles of where the enemies would spawn, and then just bang-bang-bang picking three or four enemies of in quick succession. That was really satisfying when I did it ^_^
I think this game was created very well gameplay wise. For example, the fact that you can walk around and shoot a bit in the main menu is great, because you can see the controls and try them out. This way you wont be surprised during gameplay. The only thing that was a bit confusing to me at first was the special, because it was different each time I used it. Eventually I figured out is was randomized each time, and that the little symbol above the lightning bolts indicated it. Maybe it would be nice if you could practice this in the main menu as well?
Otherwise I think this was really good and a lot of fun! The difficult scaling was perfect, and the upgrades were very impactful, but not overpowered. Great balanzing overall! The boss was very difficult for me, and I did not manage to bit it, but to be honest I think that is fine. The final boss is supposed to be difficult :)
I see know that you started learning game development only three months ago, in which case this is even more impressive! I think you already have a great grasp on important things such as player feedback, difficulty scaling and balancing. Really well done and good luck with your further game dev journey! ^_^