Not bad. The controls are a little clunky, but once you get used to stabilizing with the space bar it becomes rather enjoyable. It gets you to concentrate and to not be too hasty, I like that.
However it is a little short but you did mention that you planned to add more levels. I would suggest more obstacle blocks (e.g a block that you bounce off when collided with) and more themes. the whole red block with blue backgrounds can get a little dull after a while. also some change in music for the themes would be nice.
Like I said not bad!