As far as I can tell, The Shack is a book intending to help people answer the most common complaint God "has" to face. If He is good and loving, why does He allow evil?
Basically, the book revolves around the main character trying to come to grips with a family tragedy and God comes near to him, invites him on a real spiritual retreat. God proceeds to tear down all his preconceived ideas about who He is and the way things are to be.
Does the author do a good job of this goal, to defend God? I think he does. Whether God wanted defending, I don't know. That isn't really the question I suppose. God does come out as the good "guy" in the end. All the way through, God moves closer to what we would like Him to be.
That is the problem some have with the novel though, at times it was for me too. Is God becoming who we want Him to be, or does He just exist, outside our ideals? I'm not suggesting that the writer wanted to "dumb God down" for us. I don't think he has an inferior god to the one of the Bible. I think he truly wants us to see a part of God that many in the church may see as over-played already (Is it possible to over-play a part so beautiful?), His love. The writer is searching out the alienated, the fatherless and downtrodden, to point out that God is not a cosmic kill-joy. He really does love.
Is part of His character down-played in the book? Yes. Is there a danger in taking this book as a commentary on Scripture or the nature of God? Yes. Let us not forget that this is a novel and treat it as we would any other work of fiction. Use what is good for our own enjoyment and even betterment, and leave the rest as poetic licence.
God, of course, was there before us, and will remain, unchanged, after we've moved on.
Young ends up with a god who is deeply human. This is not God as Jesus either. This is God the Father. He talks like us, even less like some of us who try so hard to be pharasaical, er, um pious I mean. This was likely my most troubling point. Can God be this human? I think that as far as the Trinity is concerned, we know that He did. Jesus came here, God with human skin. The many appearances of God in the Old Testament are usually explained as being pre-incarnation (before birth) appearances of Jesus. I wonder about Moses in the crack in the rock. Was that Jesus? It doesn't appear to be so. How do we explain that? This may mean that God does make physical appearances, but it raises still another issue. Why doesn't the main character fall down in reverence in His presence? That side of God is missing, though the author is not really aiming at disclosing that side of Him. We'd give that kind of freedom to a theologian writing about the justice or love of God. Perhaps there is room for that freedom in a novel as well.