I like this, except I'm really not a fan of needing to rapidly tap a key to move repeatedly in one direction. I don't know how many shortcuts were needed to get to 256 bytes, but I think the game would benefit from significantly shorter key repeat.
The repeat delay is actually controlled by your OS here because it's just a simple onkeydown event. Implementing movement rate would require far more code because you need up and down listeners and a state.
