Fun little game. I liked it. It reminds me of my game that I am currently developing.
I do not know if you will update the game or not, however I will still leave you some feedback, even if you will not continue with the project it might still be useful for your future projects.
Firstly it is nice that you have volume slider, however I think in this case it was redundant. Afterall you can always set your volume on your laptop, I don't have to do it in your game. It would make sense if you allowed to change volume of music and volume of other sounds, that would make more sense. In short I would either create 2 separate volume sliders one for music the other one for sounds, or I would omit it completely.
Another thing is that after I found nice volume I wanted to keep, and after dying when I got back to the main screen, the volume started playing loud again (cause my laptop volume was high, however I used your apps volume slider to make it rather quiet, so when I went back to main screen, it started to play really loud). So in the end I ended up keeping in-game volume at max, and only ajdusted volume on my laptop.
Also I do not think using Shift for shooting is good idea, since I am using my right hand for the movement (arrows) than I cannot really comfortably use right shift well, so I have to use the left one. And since I keep my left hand on Space, for jumping, when I want to touch left shift, naturally I will use finger closest to it which is pinky finger. And of course pinky is pretty weak and slow finger, so using him for fast-pace shooting is not very enjoyable experience.
And also when you press shift too fast too any times you will get that annoying Sticky keys prompt.
As well I noticed that after shooting fast the bullets are kind of pushing each other slightly out of direction.
However I like the tempo and concept of the game, and the fact that the game after a while gets faster.
Nice job!