Excellent work you've done here!
Okay, I'll admit it. It isn't nearly as hard as it should or could be, but when you die it is your own fault for ... you know, dying. The star off is actually because spike blocks instantly kill you no matter where you come at them from, and the art should reflect that. Also you cannot jump without double-jumping first, and there are ways of showing this in the earlier levels, even without explicit text mentioning this.
Still, the fact is (when you grasp the concept) once you die, it's your fault, and that's what makes a good hard game in my opinion. I am interested in seeing what new levels you come up with.