Excellent. Read various times. Just listened to an audio version in the fall of 2015. Although I have read this book multiple times, the last time through on audio, I noticed that the last section contained layers I had not ever really understood. I listened to it again (Jan. 2016) with that in mind, and yep, definite layers. This book is deep.
Listened to it again in October of 2016. And yet again in July of 2017.