I think this game looked beautiful and really well executed! The enemies felt fair and not too easy, the shop had upgrades that actually made a difference. The music fitted really well, and the lighting looked great! I also really liked how you made the enemies very clear through the darkness
The main thing I think this game could improve upon is the game feel. With this I am effects that communicate to the player that something happened. For example, the first time I played I did not even notice that I was taking damage because the effect was so subtle. Something like a sound effect, or a red vinette around the screen, or more particles would have helped a lot I believe. Also during the boss fight I did not really know if I was doing the right thing, because there was no indication whether the boss was taking any damage. Some more feedback there would help a lot as well. Another thing which I find to be extremely effective is screen shake. I am always amazed at how much 'uhmpf' it gives and how a game can actually become more fun to play by just adding screenshake.
But those are just my thoughts. Hopefully they are somewhat helpful :D Thanks a lot for making this! I enjoyed it a lot!