Looper, a futuristic movie about time travel, believes that children are our future and openly shares that old-fashioned sentiment. That may be the funniest paradox in Rian Johnson's new film. Others are less amusing.

Looper has two distinct movements: in its first half, it is a fast-paced action film; in its second, it becomes a more emotional meditation on destiny, especially as it applies to raising children. As a statement, this is brilliant: Johnson wants you to know that amorality, specifically that which drives the first half of the film, does not come for free. As a viewing experience, this is jarring and not quite successful. Looper goes fast, hits a wall and then spends the rest of its time scraping you off slowly.

It's a letdown from its initial high, which chronicles the career of Joe (Joseph Gordon-Levitt) an assassin in the year 2044. Joe is a "looper," and his job is to shoot people that have been teleported in from the future, where it's virtually impossible to get rid of bodies. Joe does this in broad daylight, seemingly unperturbed by his job as a killer. No one is, mostly because in this vision of the future it seems that the options are either to kill or be poor.

Adding to the nihilism is the fact that loopers have expiration dates, and they know it – when they are no longer needed, loopers receive and kill their future selves. They're then given a pile of gold and 30 more years to live. We see scenes of loopers who just did the deed ("closing your loop") and they are celebrating, ecstatic young retirees whose lives will end in not a lot of time at all. Amorality has a price, but willful ignorance is a hell of a drug – and so are the narcotic eye drops these people take to cope.

When it's time for Joe to close his loop, he's literally confronted with his future via Bruce Willis as "Old Joe." The metaphor is too literal to be graceful, but Johnson is deft at explaining without spoon-feeding. Via voiceover, Joe runs down his complicated job in a few, clear sentences and throughout the film he gives us key terms — in addition to "closing your loop," there's "letting your loop run," which happens when you fail to assassinate future yourself. That is exactly what goes down between Joe and Old Joe, which of course creates a paradox because Old Joe wouldn't be able to come back from the future if he hadn't killed his future self 30 years ago.

This contradiction is not lost on the film, which later subtly slips in a scene of the self-assassination going the way that it originally must have. Moreover, there are sly, knowing references to how insane it all is. Crime boss Abe (Jeff Daniels) says, "This time travel shit fries your brain like an egg," and in an excellent diner confrontation between Joe and Old Joe, the elder says of their predicament, "If we talk about it we're gonna be talking about it all day, making diagrams with straws."

The awareness is reassuring and satisfying, but it doesn't excuse the holes. Nor does it compensate for the more distracting flaws, like the fact that Looper turns into an exceptional-child movie with the introduction of Cid (Pierce Gagnon), a telekinetic ball of rage that may have a key role in Joe's destiny. Young Joe's association with him occurs as a result of hiding out on the farm of his mother Sara (Emily Blunt), and her character composite as a protective mother and sexual distraction for Joe is infuriatingly predictable. This is a movie about the future, and we've seen that before. Looper is better than that.

It's also better than the horrible makeup applied to Joseph Gordon-Levitt's face that's supposed to make him look more like Bruce Willis, but just makes him look like a Botoxed Planet of the Apes extra. It's such a bizarre move, especially in what could be a crucial movie to his career, given its reception and that there's not much else out right now that hits the cerebral-action buttons Looper does. Gordon-Levitt's impersonation of Willis – the smug smirk, the way he talks to people out of the corners of his eyes – would have been sufficient.

It seems like a minor point, but it's distracting – it took me a few minutes to stop freaking out about a perfectly handsome 31-year-old getting work done ("Is it the big screen? Is that why I didn't notice it on Saturday Night Live?"). After that, I spent the rest of the movie wincing at the makeup job. The structure of Looper suggests that it would rather you feel it than really think it through, but sometimes the latter is unavoidable.