A good game, if a little short.
I personally thought it wasn't too difficult, except for the 'Hardest Level in the Game' level, and this is where my one complaint arises. I can't really describe it easily; the best way I can put it is that the hitboxes are extremely unforgiving. Many a time I found myself thinking I'd made the perfect jump, when in fact I'd brushed against the very very edge of the sprite and died. Understandably, the difficulty is what the game is supposed to be about, but it feels slightly more like it's the game's fault for your death rather than player's, though not too much.
Ultimately, the game controlled reasonably well, and even with the low difficulty, held me to the end. The music also gave a nice atmosphere, giving the game a nice, calm, creeping feel, which I think mirrors the way it's supposed to be played quite well.
4/5 stars from me, great game.