About checkpoints: I know it's just a demo but in the full game I think it's a good idea to have a checkpoint after each new major challenge. It's easy for you because you've been programming and testing it constantly but for a new player you spend ages trying to get through the bombs and then you encounter the boulders. Something you haven't seen before: do you jump over them? on them? freeze them with charge-up? Oops, too late you're dead. Back to the bombs. You know? <img src="smileys/smiley36.gif" border="0" align="middle" />
In later levels, when the player is used to the controls and the gameplay, you can string challenges together without checkpoints to make it more difficult.
It's a fun game. I'm close to killing that gorilla.