Looper is the slickest of action/sci-fi hybrids -- another piece of evidence that Hollywood, even as it borders on self-parody with its blockbuster offerings, will also nurture creative talents who are self-aware on a meta level. It is well written and paced. The two principal stars, Joseph Gordon-Levitt and Bruce Willis, take the compelling material and run with it. If you want clever, highbrow science fiction, well, here you go. You can't really complain that there's none of it around these days.

Yet at the heart of Looper there is a more basic challenge, one, that to me at least, is more familiar in another genre -- horror. The film's most memorable scene is a tense showdown between Gordon-Levitt and Willis at a dusty diner in rural Kansas. Both play the same character, Joe. Willis has traveled back in time to stop a dangerous crime boss known only as The Rainmaker. Unsure of whether to help Willis in his quest or to "close his own loop" by killing his future self is Gordon-Levitt. Young Joe has questions for Old Joe, but Old Joe insists there is no time for him to answer them. Time travel is "messy," he says. Let's keep moving, kid.

Thus, through Willis, is an elegant bit of reverse psychology planted by writer and director Rian Johnson that grows and grows as Looper hurtles toward its conclusion and sticks with you long after the credits roll. Johnson serves two masters, and serves them pretty well. On one level,there is the action and suspense, the struggle between the two Joes and the crime syndicate furiously trying to close Joe's loop. On another, there are the mind-bending implications of time travel. In the latter regard, Looper sticks to a simple set of rules, doesn't cut any corners and, very probably because of that, leaves you with about 1,000 questions about time travel and about what happens to the two Joes because of it.

This movie has been marketed extremely well, so if you've seen the trailer you know the fundamental premise. Just in case you haven't, though, a quick recap: the year is 2044 and Gordon-Levitt is a hitman who kills targets sent back from 30 years in the future, where (or is it when?) time travel has been invented and quickly made illegal. Time travel is thus only utilized by mobsters, who send victims back to Loopers like Joe for elimination, a convenient arrangement since there is never a body the authorities can find. Joe and his brethren are called Loopers because eventually they have to kill a future version of themselves. Usually they don't even realize they've closed their own loop until after the fact. Their targets are bound, hooded and gagged; gold, rather than the customary silver, is strapped to their backs in payment -- the only real signal they get that their services will no longer be needed.

Old Joe gets the drop on Young Joe because he kills his captors and travels back to 2044 without the customary hood and restraints. He has good reason to do so because his captors in 2074 killed his wife, played by Qing Xu, and his only real chance to alter that timeline is by eliminating the force behind it -- again, The Rainmaker -- while he's still a small child. The criminal syndicate, led by Abe (Jeff Daniels) in 2044, pursues both of them, and their customary handling of unclosed Loopers is quite gruesome, as we learn when Joe's friend Seth (Paul Dano) leaves his own loop open earlier in the film. But things get really interesting when Willis and Gordon-Levitt begin working against each other. Young Joe, first motivated by selfishness and wounded pride but eventually by an attachment to Cid (Pierce Gagnon), aka The Rainmaker, and his mother Sara (Emily Blunt), puts himself right in the way of Old Joe's mission.

If you can tell me who I should root for between Young and Old Joe, you have a stronger understanding of morality than I. Both are motivated by admirable sentimentality and easily accessible convictions so as to create quite the dilemma for the viewer. If you can explain the time-traveling implications of the twist ending and what it might mean for everything that happens before it without getting caught in an -- ahem -- loop, well, you're an awful lot smarter than I.

All that murkiness makes Looper quite unsatisfying, and I mean that in the best way possible. I felt similarly about 2012's other big sci-fi film, Prometheus. There are a lot of questions left half-answered in both films. The big difference between the two of them is that the unfulfilled feeling Looper leaves you with seems more intentional. Prometheus couldn't get out of its own way. Looper can't get out of time travel's way. The difference is subtle but significant.