The sense of dread is palpable, especially with the special effects when the enemy is approaching. I also like the tree shadows--good use of Unity's experimental 2d lighting system.
I also enjoyed the incidental discoveries sprinkled around the map. These gave subtle hints as to the story. Also, the twisty paths are a good, thematic way to lead the player towards (potentially) significant locations.
The main drawback is that the map feels too large, especially since the pages and the enemy are the only interactable objects (that I was able to find, at least).