It is a nice little demo. The overall feel of the game is good, it feels responsive and smooth. Two points of criticism: the game has a strong vertical dimension as you sometimes have to jump into holes. But the problem is that the field of vision is very narrow. I can't see what I'm jumping into. Sometimes you die, sometimes you enter a cave. It feels kind of random. And at the moment there are a lot of restart points, but they are not marked. For a real platform game I would like to have less restarts, but I would like to know where they are. (Maybe some kind of crystal that you activate).
But overall it is nice and I would like to know how you plan to expand the game to and what you plan to do with the crystals :)