Time travel movies can be so much fun -- and so infuriatingly nonsensical.

As soon as a character travels from the future into the past -- which typically is the audience's present -- the question arises of how his or her actions change the past. If those changes affect the character, how can it be the "old" version of the character who travels back in time? Such concerns can take a viewer out of the film, sometimes because of a simple puzzle, sometimes because of the sheer ridiculousness of such a plot.

Bruce Willis is Joe -- let's call him Old Joe to distinguish him from his 30-year-younger self, played by Joseph Gordon-Levitt. The young Joe lives in the 2040s. That's the future to us, but Joe's more concerned with a further future. "Time travel has not yet been invented," he tells us. "In 30 years, it will be. It will be instantly outlawed."

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Anyone who knows anything about human nature knows it's impossible for the government to outlaw anything. Time travel is thus in the hands of crime syndicates who use it as a novel way to solve the pesky old problem of getting rid of bodies. Joe, a looper, is employed by a company that does not yet exist; his job as an assassin is to take out "the future's garbage." He does have a boss in the present, though: Abe (Jeff Daniels), who runs Kansas City, Mo. "Any other city, and that'd be impressive," Joe wryly tells us.

The future syndicate doesn't leave any loose ends. Every looper knows he'll eventually be retired. He finds out when he kills a man from the future who looks an awfully lot like himself. He'll then have 30 more years to live -- he's executed by the mob, via time travel, before he could possibly give them away. But an awful lot of loops are being closed all of a sudden. Joe's in this for the money, so he doesn't think he'll have trouble killing his future self. But Joe's a good assassin -- and Old Joe's still got the skills. When Joe and Old Joe come face to face, Old Joe knocks Joe out cold and flees. Joe has to find him -- and kill him -- if he wants another week of life, let alone another 30 years.

"Looper," as should be plain, has a far more interesting plot than the typical time travel flick. It also has a lot more tension. But it's no mere genre ride. Writer-director Johnson is one of the most stylish young filmmakers working today. His films are fun to puzzle over, and astonishing to watch.

Gordon-Levitt must live a pretty hard life to age into Bruce Willis in just 30 years -- which is funny to say, because there are actually fewer than 30 years between them. They're both great at playing thoughtful tough guys.

Emily Blunt strips off her British accent to play a single mother whose son just might hold the key to everyone's future. But, wait, does he really? Let's take Bruce Willis' wise advice and not think too hard about it.