I like the artwork, and music! Especially like how the background characters show up and change shape/color etc, really funny. I think I got the idea that you have to press spacebar when the jumper turns red, but I discovered the same bug as the other commenter where I could just hold spacebar.
Aside from that, I think it would be easier to tell what's going on if the character moved smoothly - they seem to teleport through the air and then suddenly fall on the trampoline. It's not clear if it's supposed to be reaction based or timing based or a bit of both...