Well, I guess I am a late-comer to this party, so I don't have a whole lot to add. I have been trying to figure out how to "rate" this book. I felt that any complaint as to the writing style would raise the eyebrows of the adoring, and any complaints on the theology, the eyebrows of the religious. So, after reading a lot of other reviews, I decided to use a scale from 1 "dangerous non-biblical trash that should be avoided"; to 3 "Its Fiction! And just a fable to enjoy"; to 5 "an awesome and inspirational book that has changed my life forever."
My rating is somewhere around 3.5 - 4.0 on this scale, and I am OK with that. I wasn't crazy about the writing style, and specifically the build-up to the shack visit, but once into that portion, I think the story flowed nicely. The ending was a little less dramatic than I expected, but better than a completely unbelievable finish.
I think that Mr. Young did a wonderful job discussing the trinity, and the thoughts on faith and fate were thought-provoking and interesting. I do agree that he went a little astray on the concept of evil and the ten commandments, but I had no problem with the big black motherly God (although I couldn't shake the image of the Oracle from the Matrix movie!)
I remember reading the popular book When Bad Things Happen to Good People
when it was published in the 80's and I walked away disappointed that there was no better explanation. The Shack was much more enjoyable, and emotional, and I actually walked away feeling happier, and at least a little enlightened.
This may not be a great literary work, but I am happy that I took the time to read it, and allowed myself to be moved by the story.