Love the contrast system and the planetary gravity, its a really neat way to think about the theme and shows a real level of technical skill with the engine. That said I didn't really find it that engaging to be honest - I'm not entirely sure why, perhaps its just not my type of game - in any case its pretty darn cool, I think you have nailed the brief!
Update - maybe some kind of person talking to you and you are talking back to - just to give the game some context, grounding or some other dimension beyond what is in front of you. Just a thought!