I've found it hard to talk to friends about this movie, for a few reasons. I want them to watch it, but I want them to have the opportunity to do so without knowing what happens. I want to issue trigger warnings or tell them why it is so emotionally gripping, but also to stop short of any kind of spoilers. It can be a hard film to watch - I've even heard of one viewer who had to leave partway through, though he admired it. But though it features nightmarish elements, director Lenny Abrahamson's aim is to tell a story of familial love, and show us the innocent and creative power of a child's point of view. The screenplay (by the author of its source-novel, Emma Donoghue) helps, as does a wonderfully resourceful shooting technique. You'll recognise it when you see it.

Room has moments which carry great weight and act as points of emotional release, but which might seem saccharine in any other context. It also sidesteps charges of exploitation (or gratuitousness). Jacob Tremblay is literally marvellous - I didn't find myself noting the seven-year-old's acting chops, rather experiencing awe at what his character showed about children, and their strength and imagination. The visual metaphors for both (Lego for the latter) were touching, and his voiceover kept us viewing matters from his perspective of possibility and wonder (though it wasn't to everyone's taste in the screening I attended).

In a way that supports the director's aim, a couple of major plot-points are revealed in the trailer. By all means, watch it; but if you'd prefer to be surprised, permit me to get conceptual. This movie is both about a 'Room' that contains, and 'room' that exists outside, filled with unimaginable things. The former, I would say, is the titular character here; referred to by Tremblay without a definite/indefinite article. It is also a story about family: pushing the ideal concept of family to an extreme, in order to expose what is at its core. Room has things to say about that ("He is no-one's but mine"), though it doesn't become overly unreal or experimental in order to do so. Another throwaway line I picked up on, "We have everything", shows the human capacity to get by on not-a-lot, and how the imagination can fill in the holes left by deprivation. This mirrors the camera work, which finds numerous angles inside a very limited space.

Not having followed Abrahamson's career closely, I wouldn't have recognised this as the work of the director of Frank, as the two are wildly different in tone. However, they do each contain an antidote to accusations of exploitativeness - an opportunistic use of media, and how corrosive that can be to its subjects' wellbeing. A small point, perhaps, but the sensitivity shown here is necessary for a movie that navigates harsh realities.

On to Brie Larson. A job of work that has won her a Golden Globe (and may claim an Oscar too), her performance is totally pivotal to the film's success. Her character's mental strength, generous parenting, humour, despair, terror and joy are an opportunity for a master class in how to run the acting gamut, whereas a less assured actor might be tempted to be showy and de-centred, and thus stand distinct from the narrative context. The fact that Ma can't succumb to melodrama is integral to her dealing with the situation, and Larson's ease with Tremblay is remarkably convincing. "She and Jacob deserve some credit for each other's performance," said writer Donoghue, who was involved on set.

Credit where it's due, then, in this story of mutual support. Oscars nominations are also pending for Best Picture and Directing: I would like you to go and see why.

Room was snapped up by Irish director Lenny Abrahamson after the novel upon which it was based, itself inspired by the Fritzl case and others like it, was read by book groups the land over.

It's a remarkably faithful version, perhaps as a result of Abrahamson having fellow Dubliner Emma Donoghue adapt her own novel for the screen.

The first act is a skilfully directed one location exercise in claustrophobia. It takes place entirely in a modified garden shed, in which Joy (Brie Larson) and her young son Jack live, and have lived for Jack's entire life, and the past seven years of Joy's.

Abramson's approach was to shoot each bit of the room as if it were an independent location in its own right, thus finding several ways of capturing the space and preventing the feeling of over familiarity.

The somewhat different second and third act maintain the intrigue, and perhaps the film's greatest achievement is the discipline with which nothing is revealed to the audience unless it's through Jack's eyes or ears.

There are problems: like most American and Canadian films involving children it cannot help but be sentimental, and there's a moment at the end that seems rather far-fetched.

None the less, it's nice to see a well-constructed, honest film that also has the intriguing idea of placing such big name stars as Joan Allen and William H Macy in supporting roles that do not feature until the final third begins.