I have not read the book myself yet (but I hope to read it at some point in the future), however I have listened to what I personally consider to be a theologically and biblically disturbing interview that William Young participated in, in which he discusses his own theological beliefs.
Although I disagreed with practically everything Young stated in this interview about what his beliefs are (including his definition of Hell as not being separation from God, and his belief that people might have a chance to accept Christ after death), I will just mention the one I consider to be the most dangerous - and that is he own admitted rejection of the penal substitutionary atonement of Jesus, which he states at nearly the mid-point of the interview (I will link the complete interview below).
I am sure there may be a minority of people on this site (both Christian and non-Christian) who also reject the penal substitutionary atonement, so my audience for this post (and warning) is directed to the majority of people here (including myself) who identify the penal substitutionary atonement as the Gospel itself. The person doing the interview (Baptist pastor Kendall Adams) rightly responds to William Young by saying the penal substitution of Jesus is "the very heart of the Gospel."
So again, I have not read the book, and therefore I don't even know if William Young's denial of the penal substitution of Christ appears in the book or not (perhaps those here who have read the book can clarify if he includes it or not), however my point here is to urge Christians to be very cautious when recommending a book to other Christians (especially to non-Christians) of whom they do not know the background beliefs of the author himself/herself. And in that light, Christians should then be extremely cautious when the author publically rejects not simply "a belief" of the Christian faith, but a belief that is the absolute core of the Gospel itself.
Here is the link to the interview, which is located on the blog of David Westerfield, and is found at the top of the blog post.
I hope it can help the discussion here on CC.
Shack Author William P. Young Explicitly Denies Penal Substitution (MP3) | DavidWesterfield.net