It's excellent. I'd definitely recommend it to anyone who'd enjoy an intelligent new angle on the horror genre. I'll be giving it to Dad for Christmas, but I'll also be censoring the DVD cover. I have scissors. Radio Times quote? Plot synopsis on the back? Dad's copy of the DVD sleeve insert is going to have bits cut out of it.
It's not that the film's twist-dependent, or anything like that. It's not. You know everything after twenty minutes anyway. It's just that we shouldn't know what's going on at the beginning and I want to preserve Dad's ignorance. If you don't know the film's premise, then those first twenty minutes will be even more compelling as you gradually piece together the horrific truth.
Sennia Nanua plays a clever, polite little girl called Melanie, who lives in a concrete cell and is regularly strapped to a wheelchair so tightly that she can't move her head, let alone her limbs. Soldiers monitor her ferociously, pointing rifles in her face. Not pistols. Rifles. They don't like her. They'll be the reason why Melanie thinks "frigging abortion" is an everyday word.
Melanie doesn't let this get her down, though. She's super-polite to everyone. (I'm not convinced the actress quite managed to make all those formal terms of address feel natural, but that's a tiny nitpick in what's otherwise a top-notched, detailed, mature performance that easily carries the film.) Melanie's clever. She knows all the answers in class, when twenty children are wheeled into a room together for lessons. She's a knowledge sponge, in fact, which sometimes made me laugh. She adores their teacher (Gemma Arterton), who's more compassionate than the soldiers and so is more likely to forget and put herself in danger.
The base has one more important character, played by Glenn Close. You can think of her as a mad scientist, except not mad. Everything she does is rational and for the greater good. She knows that sacrifices have to be made and she's willing to make them.
The film's first act is its most distinctive. Those children in that classroom are quite an image and it's easy to empathise with Melanie. Personally I found its scary moments scarier than the more generic stuff later. It also has some ghastly realisations, e.g. the numbers. However the situation does change eventually, as situations are liable to do. That's fine too. It's all solid, absorbing stuff that moves the film forward. I particularly liked Green London, which is taking a familiar idea further than we usually see. (Apparently some of the footage was shot with drones in the Ukranian town of Pripyat, which has been uninhabited since the 1986 Chernobyl disaster.)
The characters are intelligent, with the soldiers in particular being downright genre-savvy. They believe in extreme risk avoidance. (Their attitudes towards Melanie evolve, though.) Scientists are capable of doing alarming things, but that's been true since the start of the film.
It's Melanie's film. Damn, she's smart. She's what makes this film special, as something so scary is also so sympathetic. I also approve of the ending. I can't say more because of spoilers, but it's perfect and exactly right.
I have a colleague at work who was recently praising the book. The film isn't an adaptation and the book isn't a novelisation. They were written together, although the book apparently has some elements that the film doesn't (e.g. junkers). If it's like the film, then I'm sure it's top-notch. I can't think of anything I'd change about what I've just watched, although be warned that it's wildly unsuitable for children and the squeamish.