The initial book shelf alike screen is very impressive. Several cool details: the blurred background is actually move when you tilt the phone. Facebook paper got some buzz for this feature, but Dcovery has this long ago. The place number change animation is also cool.
After a book is tapped, it's a little bit less cool, but still very well crafted.
A useful small feature is it show a localized card of message for you to ask for locals, or taco drivers.