I enjoyed the game!

• I like the upgrade system because it brings variety
• I like the art style and music
• I like that you added the dash cooldown as a "headband" (good visibility=

Some things that I found initially confusing:

• The upgrade system wasn't intuitive for me, e.g. only the first slot is equipped, and the others are just storage (I understood it after reading your description, but it would be nice to make it more visible in the game.
• It wasn't clear what all these different icons in the shop mean (perhaps a tooltip would help?)
• More often than not I misinterpreted the "coins" as enemy bullets and tried to dodge them and run into enemies because of it :P 
• I didn't really notice when I got hit because there is no feedback (sound/visual), just the HP on the bottom-left which is hard to see when it gets stressful
• It would be nice to regain health somehow