The book tells the story of one man's intense tragedy, years of ensuing "great sadness" and his meeting with God one day which leads to some profound changes in his life spiritually and emotionally. It is a story profound compassion, forgiveness and healing that also manages to weave some pretty deep theology into the mix.
Eugene Peterson, the translator of The Message paraphrase of the Bible as well as the author of several books on pastoral theology says "This book has the potential to do for our generation what John Bunyan's Pilgrim's Progress did for his. It's that good!"
Like Pilgrim's Progress, The Shack is heavy on matephorical/allegorical imagery. This is a book I would call an exercise in stretching. Whether you perceive yourself as conservative or liberal, orthodox or unorthodox, modern or post-modern, evangelical or emergent this book will stretch you at some point in your theology. Sometimes stretching can lead to breaking but with The Shack I think the stretching is actually a good and potentially beneficial exercise.
At its most helpful The Shack offers a refreshing interpretation of the Trinity and what forgiveness and a healing journey with God might look like. At its most controversial (stretching) it offers some strong words about institutionalized religion/Christianity and a strong affirmation of the orthodox understanding of creation.
Scattered with quotes from a variety of people including A.W. Tozer, Dostoevsky, C.S. Lewis and Bruce Cockburn I believe The Shack will become an excellent resource in grief counseling and I highly recommend it - especially for book clubs and/or study groups.