Interface destroys the game. Whenever I tap anything on the book, it takes forever for the spirit to come out and say hi before I can do stuff, and when I close it, it takes forever for the spirit to go away.
I found this a major annoyance since you'll be doing a LOT of things on the book, and those little hindrance add up pretty quickly.
Minimap is poorly done, it doesn't tell you if an edge of the map leads to another map or is an invisible wall; you're in the middle of a grass field and minimap gives no indication that you can't progress East but your character will get stopped by an invisible wall if you try.
The concept is very creative, but not well executed enough.