I played several times and got up to 37. The game is pretty easy to pick up on considering is only uses one button/key to play.
I think the main improvement that you could make (besides adding graphics and audio), would be to add some type of damping/interpolation code function to the player movement. Right now when you press the W key the movement is immediate. It would be nice if there was some acceleration instead of immediately going to top speed when pressing and releasing the W key. This would give the whole experience a much smoother feel to it.
This one is a lot of fun and very easy to pick up and put down. If you do put more time into it you could even make levels that unlock once you finish the current one or get past a certain time on a level.