This is a Best Dramatic Presentation, Long Form nominee for the 2015 Hugos.
This is not a movie with any deep thoughts in its head. It's pure, fun, over-the-top adventure, with colorful space battles and explosions.
Peter Quill is kidnapped from Earth as a kid in 1988, and raised by an interstellar criminal gang. As an adult, he steals a mysterious orb sought by a fanatical opponent of a recent peace treaty, Ronan the Accuser. After some entertaining and bizarre events, Peter, along with Rocket the genetically engineered raccoon, Groot the walking tree creature, and Gamora, a trained assassin whose adopted father Thanos hired her out to Ronan, wind up in prison. It's after they break out together, having picked up Drax, who wants to kill Ronan, along the way, that things get really dangerous. (Fortunately, Gamora would also rather kill Ronan than work for him.)
It turns out the orb contains an infinity stone, which will let its possessor destroy whole worlds. Ronan, who quickly gains possession of it because the accidental allies are working at cross-purposes, wants to destroy the world of Xandar. And Xandar would be just the beginning.
Suddenly, this collection of criminals has a big decision to make about just how careless of morality they really are.
Also, of course, they need to convince the authorities that recently had them locked up to listen to them.
Guardians of the Galaxy is a lot of fun. Best science fiction movie of the year? No, I don't think so. But seriously, a lot of of fun. Too late to catch it in the theater, but rent it or find it in your cable system's movie offerings.