I liked this game. There were a few places where it felt like the controls were missing, though.
I wish that the up/down arrows would let you walk along the walls like the left/right arrows do on the floor and ceiling. Using the left/right arrows on the walls is very unintuitive. I also wish that the character would face in the direction that you're walking. This would only really be relevant to the boss battle to let you aim, but it'd make you feel a lot more in control of the character.
The final suggestion I have would be to reduce the randomness of the boss. Give it some sort of behavior pattern in the way that it moves. That'd give the player an opportunity to figure out what the movement pattern is, and let them feel clever when they come up with a way to exploit that pattern to beat the boss.