Sad to say, a lot of Christians will give this book a break on its bad theology because it's allegedly such a moving story (though I found it to be poorly-crafted literature as well). And I will give it one break, inasmuch as it does make use of some of the same arguments you'll find in Glenn Miller re the problem of evil. But none of this makes up for the way in which The Shack swims in the "God is my buddy" emergent riptide.
How bad is it? Very bad. The lead character's wife calls God "Papa" and claims to have an "intimate friendship" with him. All three members of the Trinity are presented as giggly, fluffy people who can't stop hugging and kissing the lead character, and each other, and act as the lead character's personal grief counselors. Young no doubt wants critics to fall into the trap of objecting to the specific racial and gender forms he has them appear in, so he can accuse the critics of bigotry -- sorry, no. It does need to occur to him that it's no more helpful to remake God in an image for the sake of a social agenda than it is to portray Him as a white man.
I have written repeatedly of the view of God in the Bible in terms of an ancient patron -- remote and indeed one who seldom makes direct contact with, or interferes with, His creation. Works like Young's will only further alienate Christians and create apostates as they come to realize that THEY will not be receiving personal messages and counseling sessions from God the way the lead character does.
Despite Young, it is NOT about "relationships and simply sharing life." (178) The only "relationship" the Bible offers with God is a patronage relationship -- one in which we serve. There are no bag lunches with Jesus and we are not here for the experience. It is not a "living friendship" -- this has been imported into the faith based on Western models that have emerged only in the last 100 years. It's also not about rules, as Young portrays the other side of the equation; though it suits the emergents to empahsize when that is done so that they can propound their opposing and more egregious error with greater ease.
And to make matters even worse, Young refers to the lead character's seminary training in derisive terms (though all of his "argument from evil" material would have come ultimately from the likes of Plantinga). To wit: "...God passing notes did not fit well with his theological training. In seminary he had been taught that God had completely stopped any overt communication with moderns, preferring to have them only listen to and follow sacred Scripture, properly interpreted, of course. God's voice had been reduced to paper, and even that paper had to be moderated and deciphered by the proper authorities and intellects." (65-66)
But it DOES have to be so moderated. Young shows precisely WHY this is the case in his contrived, emergent rewriting of the members of the Trinity as giggling goodbuddies and his incautious endorsement of direct phone lines to God (the Mormon burning in the bosom is about as efficient). Not to mention his egregious errors of failing to recognize functional subordination in the Trinity; of having Jesus say he didn't intend for people to follow him as an example to copy (149 -- wrong; that would have been Jesus' function as leader of his ingroup; and what of Paul's admonitions to imitate Christ?), and of failing to connect Proverbs 8's figure of Wisdom with Jesus -- instead, he makes it into yet another of God's hypostatic entities, though not one on a par with the Trinity (171).
Of course, since people accepted Dan Brown so uncritically, there's not a lot of hope they'll be any more critical when it comes to The Shack. To me, it's just one more source of error to correct aming thousands.
Another excellent review of the book may be found here.