The sound loop is a bit short but not so much that it gets annoying and it does sound good. The sprites also look great and the controls where nice.
I do like the little hints you gave. Made it obvious what to do for people like me who don't really play platformers. I also don't think it was too short. At least, not for a gamejam game. You showed your mechanic, played a bit with it and left before it got boring while leaving behind a challenge for those that wanted more.