It's nothing less than shocking that Ender's Game any is good at all. Stuck in development hell for something like three generations of fans of the Orson Scott Card novel from 1985 to grow out of its target audience, and finally given the breath of life by a writer-director as dubious as Gavin Hood (of the admirable and sluggish Tsotsi, and the outright foul X-Men Origins: Wolverine), the film comes pre-loaded with a whole lot of baggage that should absolutely murder anything that's even vaguely keeping its eye on a popcorn-movie audience. But it is solid: surely not the best film that the book could have produced - and I should clarify right this minute that I have absolutely no stake in the book whatsoever (came to it far too late in life to form the sort of rabidly enthusiastic attachment it seems to engender) - nor a completely rock-solid science-fiction movie totally independent of its story. But it works, and impressively, it does not short-change hefty thematic ideas that are far darker and morally complicated than the film's generic trappings suggest as a realistic possibility.

The story takes place in a militarised future, half a century after humankind won - barely - a war with an insect-like alien race referred to as "Formics". From what we can see, everything about civilisation has since been directed with laser-like intensity toward building up enough defensive capability to fend off what is widely perceived as an inevitable second war with the Formics, from the education system to the mass media to population and resource control. Our main character is Andrew "Ender" Wiggin (Asa Butterfield), a boy of about 12 years, who is a rare (in this world) third child, with the implication that the government permitted him to be born in order to harvest him for its military training program. This is where we meet him, shortly before his quick instincts, capacity for tactical thought, and a violent streak tempered only somewhat by compassion bring him to the attention of Colonel Graff (Harrison Ford), who is looking for, essentially, a Chosen One. For the current military thinking is that it makes sense to put adolescent children in total control of all tactics, since they are less likely to be encumbered by preexisting notions of what is good and bad strategy. I think we can earnestly debate whether this makes any sense at all, but it's always the fair thing to spot a story its concept, especially when the concept is presented so early as it is here, giving us plenty of time to get used to it.

And so Ender rises through the ranks, making enemies of some cadets and friends of others and setting himself out as quite a special, strange child in all ways. Because, by all means, this is a Chosen One narrative, and not much interested in changing the rules, though it does tweak them something fierce with a series of questions that are voiced more openly and frequently as the film moves on, about whether or not it's even a little bit okay to turn children into murdering psychopaths in order to defeat an existential threat. It's a little bit frustrating how the film shifts from presenting this idea obliquely to presenting it emphatically, especially when the ambivalent Major Anderson (Viola Davis) states it outright in little words. But this is a mainstream space adventure, and philosophical subtlety wasn't on the table to begin with. Let us be grateful instead that something as superficially glossy and inane as this manages to sneak so much honest-to-God moral reasoning in underneath the CGI explosions.

For it is, undoubtedly, glossy; and there is, assuredly, much in the way of CGI. Though honestly, it's kind of a rinky-dink future that Hood and production designers Sean Haworth and Ben Procter present us with: I admire that it seems beholden to a style of movie futurism that feels like it was made, itself, in the mid-'80s, when the book was brand new, but that certainly doesn't change how unbelievably typical everything looks (glowing panels on the walls, tubes of light marking shapes, steel grey everything), no matter how much the whirling camera wants to convince us otherwise in its goggling amazement at every new set and its lovingly-rendered exteriors (that camera wielded by cinematographer Donald M. McAlpine, of Moulin Rouge! - the man knows how to whirl, if he knows anything). The actual quality of the work done to bring all of this to life is quite extraordinary, particularly considering the film's big-not-astonishing budget; brilliant CGI in service to dismayingly bland dreams.

Still, the movie seeks to entertain, and it does; there are space battle scenes between ships and between individual humans that are gorgeous, balletic explorations of movement in three dimensions even by the standards of the year that Gravity happened. It's the rare film with scenes that made me genuinely sad that 3-D wasn't an option; it would have been quite a spectacle.

Is that a problem, I wonder? Spectacle is great; we should all love spectacle, if we care about cinema. But there's definitely a tension between the strained, ethical darkness that makes up the film's character arc (and Butterfield does an exceptional job playing a young man with all the childhood burned out and replaced by the desire to be efficient at war games), and the lightly cheesy, blithe way that Hood and company presents it; though I admire how presenting the big action set-piece as so much cinematic junk food allows the film to wallop the viewer with its undermining twist ending. Still, just as the book has been accused at times of hypocritically endorsing the militarised world it overtly disdains, the movie has even bigger problems, since naturally enough, the handsome warfare that we see is more exciting than the warfare we read about.

And there are other, more mundane problems: the uniformly bad performances by every child actor who isn't Butterfield (including theoretical ringers like Oscar nominees Hailee Steinfeld and Abigail Breslin) certainly sucks a lot of the wind out of a film where all the most important and interesting and active characters are children. Hood's screenplay also doesn't do much more than a functional job of shifting from the inside-out POV of the book to a totally neutral third-person perspective, though he streamlines the material well enough to fit the whole thing in just under two hours. And strip out the bleak undercurrents about children in war, and the whole thing is unbelievably generic: unexceptional sets, like I said, but also unexceptional music, dialogue, storytelling beats.

It's more impressive for what it is than how it is, I guess I mean to say; and in the long run, that's not especially impressive. But as far as slick entertainment goes, this one has enough of a brain to at least vocalise ideas about right and wrong, and the more that family-friendly popcorn fare indulges in city-destroying acts of violence, the more refreshing it is to have something that actually calls our attention to that fact, even if it could certainly do a better job of it.