An interesting idea
Idea: Very creative. I'm not surprised no one has done anything like this before.
Controls: Very easy to get into. However, there were points when I found myself 'falling' in a direction I did not expect. Perhaps an on-screen indicator would help?
Graphics: Rather simple, but this is a demo.
Overall: This is an interesting idea, with great potential. I congratulate you, and I look forward to the final version.