As an atheist, this Christian themed fantasy thriller was an unusual choice. But perhaps less so, considering the missus is a Christian and so was her friend whom she invited over.
My general view is that very few explicitly Christian-themed movies, apart from Hollywood epics (including Gibson's Passion of the Christ), cut the mustard for me. The acting is often dreadful, the scripts heavy handed as can be almost every other remaining aspect of the production. I've had to sit through some right dreck while the missus makes rare allowances because of their spiritual core. On reflection, that's not unlike myself with 60s episodes of Doctor Who.
The Shack represents a rare departure from the norm. It'll never be mainstream viewing, but the production values are high, and the acting is solid. There were only few moments which felt slightly awkward to a non-believer. It probably helped to cast Worthington, who while not having the greatest range, brings some acting chops. I also enjoyed Spencer's portrayal of Papa. Accepting, grounded and gently probing, this is God as a life coach. If a relationship with God was this tangible, accessible and universal - I imagine more would do it. Perhaps AI, virtual reality and/or psychedelics will bridge the gap in the future.
Personally, I didn't find the Christian message too heavy handed - but I'm probably about as far away as an atheist can get from an evangelical like Richard Dawkins. In fact, it caused me to question some of my past perceptions. For example, that no-one may adequately judge another and that no-one ends up in hell. I can't imagine that going down too well in certain parts of the Christian faith spectrum.
A comparison I kept returning when watching this movie was the Matrix. That's perhaps not too surprising given the shifts in reality perception and themes of religious mysticism.
Verdict: Digestible Christianity