Really easy.
I think you have a lot of potential, but the game seems like it was made in a hurry. The artwork could be better, but it's the little things that seperate addictively fun games from mediocre crap games. This was really easy, even on Insane mode. Mainly because of 2 things: you can continuously drop spikes without interruption making a spike wall that the stickman walks in to winning the level, and the head is not the only vulnerable point. To make this game more fun and challenging I would make it so the head is the only point that will win the level, put a little more effort into the artwork, and put a delay between the dropping of the spikes. You've got potential, keep it up.