Great atmosphere, sound design, and music. For some improvements, I would either change the sound of jumping (or maybe change pitch every jump) or get rid of it altogether. It gets pretty annoying if you jump a lot. Also when you just start playing the game and get to the spikes, you fall down and there is no way of getting out but only to walk into spikes until they kill you, and when you do die the checkpoint is really far away and you have to walk all over again.
