-Needs an options menu.
-Menu needs keyboard support.
-Background is too plain; you need some parallax so you actually have some indication that you're moving (apart from just a vertical gradient).
-Movement isn't nearly precise enough and the camera is too close to avoid the kinds of things the game throws at you.
-What the hell is with the character floating upwards on a balloon forever after you die and forcing you to quit to the menu?
-Restarting doesn't reset the difficulty.