Very nicely done. I really enjoy the central mechanic of limiting the player to one button for moving and shooting. It leads to fun shooting and then moving in the opposite direction to avoid hitting the enemy. I think more enemy variety would be help spice up the game a lot - maybe some that play with the idea of only having one bullet in interesting ways. The game feels really good to play. Your sound effects and simple geometrical art style are great. It honestly feels like a modern take on an arcade game.