Although Looper is a movie about time travel, very little time is actually spent on the mechanics and the potential inconsistencies posed by time travel. It eventually boils down more to two love stories - a man and his wife and a mother and her child. Set in a near future, where cities are ruled by crime lords; the hero is a drugged up thug who works for one such crime lord, as an assassin.
In a longer term future, time travel has been discovered, banned and effectively only used by crime lords to dispose of bodies to a past; where they are disposed off by asssassins known as Loopers. It is a novel plot on an old science fiction classic, and most of the time travel conundrums are addressed fairly well.
While Joseph Gordon-Levitt and Bruce Willis are the main heroes (with Joseph Gordon-Levitt playing the younger Bruce Willis); the really great performance is delivered by the young Pierce Gagnon (Cid) who ties all the storylines together.
It's a good sci-fi action movie, and certainly worthwhile watching.