This week in the UK, a film opens on multiplex screens across the UK, in which the Christian message is explicitly presented. For large portions of its running time, characters talk in depth about some of the great enduring questions of life and existence, and address some of the almost unanswerable questions around human suffering and a God who seems to choose when to intervene. It arguably presents the most significant opportunity in living memory for Christians to introduce their faith to their friends through an engagement with mainstream culture. Yet so far, excitement about the film has been strangely muted, because there's just one small problem: the film is based on controversial best-seller The Shack.

There seem to be many reasons why certain vocal Christians are uncomfortable with William P Young's 20-million selling literary behemoth (a key one is probably that none of their books have ever done quite that well). Some argue that it presents an imperfect or incomplete picture of the Holy Trinity, while others worry that it wanders into the most dangerous territory of all for modern Evangelicals: the doctrine of universalism. Some critics say that Young tries to change the nature of God to answer the question of suffering, and some say that he mutes the wrath of God, which is a necessary part of the complete picture of the Father. And let's be honest, some people are just very uncomfortable with the idea that God could be a black woman.

All of these criticisms – fair or otherwise – hang around the neck of the Shack phenomenon, and can't help but colour emotions around its cinematic retelling. They mean that 'controversial book' naturally translates into 'controversial film'. But does that mean that thousands of Christians across the UK are about to let a golden opportunity pass them by?

One key part of the answer lies in whether The Shack movie is actually any good. Despite some wishful thinking and some extremely kind reviews, 'Christian' cinema over the past few years has been almost universally terrible. Poor acting, heavy-handed writing and clueless direction often combine on products pushed out to a church audience who have their forgiving natures abused by films that would never pass Hollywood's quality-control thresholds. Happily, this does not describe The Shack, which is easily the best explicitly faith-based drama I've seen, in terms of acting, direction, writing and production values.

Just in case you're uninitiated, the film closely follows the book's story of Mack, a man who falls into a Great Sadness after the abduction of his young daughter, and who can't begin to understand how a loving God could let this happen. For some divinely-mysterious reason, God decides to reach out to him, inviting him to a strange third place between heaven and earth, where Mack meets manifestations of the three parts of the Trinity. Their ensuing conversations, as Mack slowly begins to wrestle with the big questions of existence, take place in and around a re-born version of the same remote building in which his daughter's blood-stained clothes were found: the epicentre of his greatest pain.

Sam Worthington is pretty good as everyman Mack, and Octavia Spencer always watchable as the disarming Papa / God the Father. Interestingly though, it's newcomer Avraham Aviv Alush who unexpectedly steals the film as Jesus. From the moment he meets Mack in the woods outside the Shack and therefore leads him into the presence of the Father (geddit?), Alush constantly draws the viewer's focus with an understated and winsome performance. Partly that's because he's an incredibly warm and watchable presence, but it's also because director Stuart Hazeldine has intentionally created a film which naturally causes us to fall in love with Jesus. While the conversations with Papa are about justice, suffering and other big 'apologetics' questions, Mack's interactions with Jesus offer a compelling vision of friendship with God, and are the thing you keep thinking about long after the credits have rolled.

That is perhaps the most fascinating thing about The Shack, and it's what potentially makes it such an interesting evangelistic resource for Christians. While the Passion of the Christ enabled non-Christian viewers to understand the pain which Jesus endured on the Cross, The Shack illustrates the friendship that his suffering enabled. Both are important, but the latter should not be overlooked, and this film offers an important bit of balance to most of the other major depictions of Christ we've seen on screen.

It's not a perfect film of course, but The Shack certainly isn't worthy of the critical pasting it received in the US mainstream media. The book was always going to prove tricky to film given that it doesn't follow a classic narrative structure and is basically a man having conversations with the Trinity, and given the restrictions involved in adapting the material, Hazeldine does a great job of creating an emotionally engaging experience. Aside from a couple of clunky lines of dialogue, and a few awkward moments when Worthington's Australian accent occasionally pops out, it's hard to imagine how anyone could have made a better version.

All of which means that if Christians do follow the advice in certain quarters and avoid the movie, they're missing out on a powerful, thought-provoking piece of cinema which, like almost all films, is best seen on the big screen. More than that though, they miss the chance to get behind a major cultural event which – while not theologically perfect – unapologetically presents a message of God's love for the world, and the idea that he is present in and even at work through our deepest suffering.

No film, book or sermon can possibly represent theological perfection. All of them go through human filters (and don't forget that William P Young was only ever trying to write a story for his own grandchildren). Ultimately all these things can only hint at the truth about God; they're only another step in helping us to reconcile our deepest questions. It would be a huge shame if the British church didn't engage with a big-budget cinematic release that so serves it's agenda, just because it might not perfectly illustrate the nature of God. Overwhelmingly, The Shack does a great job of explaining God's love for every person, his presence in our darkest moments, and his offer of meaningful personal friendship. It opens this week, and will remain on screens for only as long as audiences support it. The question is: will the church which so longs for people to understand the very message it promotes, actually bother to get behind it? I hope we will.

Martin Saunders is a Contributing Editor for Christian Today and the Deputy CEO of Youthscape. Follow him on Twitter @martinsaunders.