Pretty well-explored mechanic by the end, even if the curve building up to the interesting gravity-reversal mechanics (which, to me, were by far the best use of your concept) was pretty slow and made frustrating by some really slow friction. For future games maybe reconsider some of the ways you implement sound - entering and exiting those gravity-reversal zones made a tone that didn't quite match the frequency with which the player would be entering them.
Make sure everything builds towards the joy of your central mechanic, which, in the end, did have quite a bit of room that you afforded it. Make sure to emphasize your strong points. : )