A goodly few find science fiction to be silly, indulgent and puerile. There's certainly plenty that's just nonsense and fluff, but the same is true of any genre. Its worth is in how it can wrestle with big ideas by changing their form so that we come at them from a new perspective. Ender's Game (the film, rather than the book) is nine-tenths fluff, one-tenth big idea. That it is, for the most part, fluff isn't entirely director Gavin Hood's fault - it's just mostly his fault.
Condensing the set-up of Orson Scott Card's novel into a paragraph is probably futile, but here goes: Ender (Asa Butterfield) is being trained to become a master tactician because of an attempted invasion by an alien race 50 years before his birth. He's sent to battle school, which is on a space station in Earth's orbit. (Half of you will have already started to tune out, but stick with it.) The literal and figurative centre of the school is the Battle Room, a zero gravity chamber where the cadets fight. There's no up or down, no east or west; tactically it's brand new territory. Which is why Ender is so important. He's young enough to set aside his preconceptions and fight in a way his elders could never imagine. This is all just lead-in. What's at the heart of the story is the quote during the opening credits: "In the moment when I truly understand my enemy, understand him well enough to defeat him, then in that very moment I also love him." Ender is being turned into a weapon, but to become the perfect weapon guarantees he'll be a weapon that'll never fire, because how can he destroy what he loves? That's an interesting idea right there, and it's what Hood is supposed to be exploring. What he's actually done is produced a CliffsNotes version of the novel: it hits all the major story beats, but is ultimately lifeless. There's no tension to any of it. No risk. Instead Hood spends the first two-thirds of the film shouting about how the aliens WILL come back because, um, because they WILL! Which isn't a particularly good stand-in for actual tension.
Frustratingly Hood manages to get the hardest things right (the casting of Ender and the immaculate design of the Battle Room) but drops the ball when it comes to basic storytelling. He sprints through the story to suggest narrative momentum where there is none, and in his rush forgets to explain things that would help us connect with the impossible things we're seeing (the most notable thing to go unexplained is how battles are won or lost (or even fought) in the Battle Room, which is a rather crucial bit of info - if we don't understand that then we don't understand why Ender's as good as he is).
Hood is a workmanlike director, usually better suited to grounded dramas (Tsotsi) than anything sci-fi inflected (X-Men Origins: Wolverine). Here he simplifies Card's award winning book to such a degree that it'd be indecipherable to any who hasn't read it. It's only in the last few scenes that the film seems to escape its first act, finally telling the story it had been hiding in plain sight. But then it ends, and the credits roll.
Overall: 4.5/10
Minor spoilers! (highlight to read)
In a flashback/stock footage of the alien invasion we do battle against the invaders with fighter jets. Not futurist-type ones, but the ones we presently use. Jump forward 50-years and our tech, particularly that of our spaceships, is so powerful it would give Lord Vader and his Death Star pause. How did that happen exactly? And how did we build them and send them many many lightyears into the aliens home system by the time the story starts? From what I remember of the book this isn't an issue as we do battle with tech of a comparable level. Not sure why Hood changed that. It just adds to the film's many problems.