Thanks for playing and the feedback! :)
Yes, level 4 is a bit on the hard side, because when they fall down you have to bring them up again the whole level again. I wanted to add a puzzle that also requires some timing but recovering from failing in this case is not very good. I'm already working on version 1.1 to address many of these issues. I have to see if I can do something about the jump buffering though, but I will add it to my to do list!