I really loved this entry, got stuck playing it for more time than i expected hehe! As a fan of racing games a think this ideia is really unique, it gives a very nice twist on the genre adding another completely different thing for the player to control and pay attention. I think that if you continue to work on this project (which i do hope you do), you should warn the direction in which to turn a little bit earlier, since a lot of the portals are right before some fast turning points and in the beginning it was a little bit difficult to make the turns. With more levels/modes and additional controls (like maybe going backwards or drifting, like other games) i would definitely buy and play it a lot!!
Very solid work and fun game, hope you keep it up!!