Let's start here: What's a looper?
Glad you asked.
In 2042, time travel hasn't been invented yet. But in 2072, it has, and it's also been outlawed. So it's used by the mob to send the people they want to dispose of backward to 2042, where guys called loopers get paid a lot of money to off them in cornfields with huge guns called blunderbusses.
Joe (Joseph Gordon-Levitt) is one such looper. The city where he lives in 2042 has seen better days: for the most part, life here is the proverbial nasty, brutish, and short kind, even for the 10 percent of the population who have developed the strange ability to make quarters float with their minds. Their motorcycles are more like hovercraft and their technology is advanced, but there are plenty of people who live in housing projects covered with graffiti and scavenge for a living. The high life for someone like Joe, whose stash of silver from his job is impressive and growing, is mostly found in fast cars, late nights partying at clubs, and taking drugs through eyedrops—all with fellow loopers, like the hapless Seth (Paul Dano). Seth and Joe work for Abe (Jeff Daniels), who was sent from the future to run the looper operation.
Life is an endless cycle of partying, paid sex with women, drugs, and jobs with the blunderbuss. But then one day, loopers start discovering their victims are, well, themselves—thirty years in the future. This has happened before—they call it "closing the loop"—but now it's happening more and more frequently. Rumor has it some shadowy figure in the future called "The Rainmaker" is closing all the loops.
And then, one day, Joe comes face to face with his own loop (Willis). Who knocks him out cold. And then escapes.
Sci-fi films have a persistent problem: they start with a great, mind-bending concept, but when it comes to execution, things like character development, plot, and follow-through often fall by the wayside. The result is a fun, even fascinating, but generally half-baked film that needed a few more revisions before making it to the public (see also Push, Prometheus, Source Code, etc.).
Looper, thankfully, is not that film. Director Rian Johnson's first film, Brick, was high-concept crime noir set on a contemporary high school campus in southern California; his second was the postmodern con-man film The Brothers Bloom, which played with the time-honored caper genre. It's clear that Johnson loves the movies and enjoys messing with established genres a bit—not to draw attention to himself, but to subvert the audience's expectations and make them see the story in a new way.
When someone decided that Johnson could handle a big-boy movie budget, it would have been easy for him to lean on special effects, futuristic eye candy, and cool technology to sell tickets to Looper. But he did nothing of the sort (in fact, in making Gordon-Levitt look like a young Willis, the production eschewed CGI for good old makeup and prosthetics—and two and a half hours a day in the makeup chair). Instead, Looper is a carefully plotted story, based on a mind-contorting concept, peopled by great characters who are played by talented actors, especially Gordon-Levitt, who is definitely the hottest commodity in Hollywood right now—this is the third of his four films releasing this year. And when neat futuristic elements do show up, they're in service of the plot. (As an aside: this is one film whose trailer, mercifully, doesn't give away the good stuff.)