Think as a demo, there is a lot of potential for this game! I like the art and music, it creates a nice atmosphere. The controls seem pretty good too, although I can't jump while pressing up and left for some reason, which is really annoying!
The frequent checkpoints are a great idea too. I tried to kill the monkeys by jumping on them, but I don't think you can, would be cool if it was a bit clearer if you could kill them or not.
Overall, I think it is good, look forward to seeing the full game!