Now I remember why I gave up on this game...
Player can jump long enough one time, and the next he will come up short. Player / enemy hitboxes are inconsistent - sometimes seems right and then all of a sudden I will be an inch of screen away from something and it will kill me. Hitboxes for terrain is inconsistent too - sometimes I will land directly on top of a box and it will "teleport" me to the side of the box so I fall off. Most of the time when I land on a box I actually land there, but sometimes I simply fall right through it. Hitboxes for spikes are a joke! I can land on a box next to a set of spikes and the spikes can still kill me?
This game is not challenging because of good game design - this game is challenging because it is unpolished.