Marvel Studios has excelled thus far by creating characters that neatly fit into segmented niches that are easily identifiable for audiences — Iron Man is the quippy inventor, Captain America is the old-fashioned moral exemplar and Thor is the seemingly immortal “alien” — but with the release of James Gunn’s Guardians of the Galaxy, all those labels and boxes get smashed.

The Marvel movie universe expands on the collection of “losers” led by the half-human/half-alien thief named Peter Quill (better known, in his own mind, as Star-Lord), proving that thinking outside the box really can be liberating. There’s a refreshing mix of devil-may-care humor (from smart 1980s pop cultural references to the seamless integration of a gun-toting raccoon and a walking/talking tree) and honest emotional investment in the backstories of these anti-heroes who wind up saving the day. By the end, the Guardians, confounding expectations, become exactly the kind of superheroes the Marvel universe needs to move forward. (PG-13) Grade: A