I do love the concept of switching between two worlds/realities, and it fits the Black and White theme really well. Big fan of the minimalist art style too, and the audio was a nice touch, although it would have been cool if the creature emitted some noise in the dark world so you could hear it coming.
The gameplay itself felt a bit limited, but obviously I understand the 72 hour time constraint! I think you could easily expand on what is there and polish it up into a really nice little game if you wanted to continue development :)