The comic book studio seems to fear that if the solemnity of its fiction isn't diligently guarded, people might start questioning whether all these men in spandex merit quite so much attention. Yet "Guardians of the Galaxy," a 3-D space opera about a ragtag crew of mercenaries, is Marvel's most irreverent film yet, and has a welcome, slightly self-mocking tone that dares to suggest intergalactic battles over orbs might actually be a tad silly. Blaring is the irresistible 1974 hit "Come and Get Your Love" by Redbone, the first of many such old radio hits. The resulting scrum for the orb introduces several more seekers: the green-skinned Gamora (Zoe Saldana), the hulking Drax (Dave Bautista) and a CGI odd couple: a bitterly sardonic raccoon named Rocket (Bradley Cooper) and his sidekick, a talking tree called Groot (Vin Diesel) who looks like he sprouted from "The Lord of the Rings." The pervasive movie references detract from the stab at freshness, and "Guardians" depends all too much on the whimsy of '70s anthems for an original beat. Guardians of the Galaxy," a Walt Disney Studios release, is rated PG-13 by the Motion Picture Association of America for "intense sequences of sci-fi violence and action, and some language.