It took a minute to get used to, but the movement felt good, the enemy deaths feel satisfying, and I like the little trail you gave to the player and the music sounds really good as well. A couple of problems, though, the escape key just exits from fullscreen (I think this is because it's played in the browser). This means I can't get to the shop. Also, the health bar doesn't seem to work. You can keep shooting enemies with no consequence of dying (which is kind of the point of the game). The game itself feels great to play though! :)