I did NOT look at the image of the map, I spent way too long trying to figure out where I'm going but I managed to get to the boss somehow. You should include the map as an introduction before starting the level. but also for future development, you shouldn't rely on like some sort of website to instruct people on how to play the game. these things should be included unless they are like super simple.
Another thing is that the movement is kind of awkward, stopping in place to shoot doesn't really feel good, and the fact that the map is so huge, I think you should really rely on moving really fast.
in my opinion I think the enemies have too much hp, but if you are going to nerf the hp you should make up for more enemies just so it is satisfying.
I like the art and music!