You got the simple visual aesthetics fine but the audio department need serious work and the gameplay needs a bit of fine tuning to be more entertaining and engaging.
Please find some audio and kick things up a bit. Let the rhythm guide the player around your game. It is a must or the game will be very dry.
For the gameplay, so touching an enemy means "game over" and if an enemy escapes to the left, it also means "game over"...
Tell you what. Since this Ludum Dare is "YOU ARE THE MONSTER", give that box the player controlling a meaner look. Give him teeth, cruel eyes, anything. Now, go find some sound of dogs with rabies for this new meaner box and pumpkin squishing sound for gore. Replace those "tum tum" stomping with the new monster and gore sounds. We got a monster!
For the gameplay, if you touch an enemy and you die, that feels inferior. Remove it. Instead, to make things more engaging, I suggest have the enemies try jumping over the player and sneak over the player at faster speed. This way, the game would feel more like you are the monster and will not let anyone escape. Let the game be over only if an enemy escape. With this, you now got yourself a cool cruel cube monster.
Sorry if I speak too much and make you feel bad but... I mean, hey, the theme is "YOU ARE THE MONSTER", so let's kick things up to eleven!