First impression was to use WASD to move, however once I learned how to play it was easy and fun to pick up. The music is super catchy. It would be nice to be able to hold the mouse button to auto shoot instead of always clicking. The overall aesthetic was very clean, polished, and vibrant. It's a simple game, but its complete so that's what makes it fun to play right away. It would also be awesome to see if the borders of the game could be removed and replaced with infinite scrolling so when your character goes to the top of the screen he would wrap back around and come up from the bottom, for example. Not sure if that would make the game too easy or too hard though, but would be fun.
Pretty cute game!