While Guardians of the Galaxy is about the formation of a team, it primarily follows the group's only human, Peter Quill (Chris Pratt, Parks and Recreation, The Lego Movie, Zero Dark Thirty). Abducted from Earth just after his mother's death, Quill has grown up in the rougher parts of the galaxy and is always looking for the next score. While he stylizes himself as "Star Lord," it's a name that hasn't really spread around that much yet.
When Quill double-crosses his crew and attempts to retrieve an artifact on his own that the entire group was supposed to steal, their leader Yondu Udonta (Michael Rooker, The Walking Dead), puts a bounty on Quill's head.
Enter the oddest pair of bounty hunters you've ever run into. Rocket Raccoon and Groot (voiced by Bradley Cooper and Vin Diesel, respectively) are life-long partners that compliment themselves just as well as Han Solo and Chewbacca, you know, if Han was an anthropomorphic, genetically-modified rodent that really likes making weapons, and if Chewie was a giant tree with that only says "I am Groot" instead of growling. While this pair sets their sights on Quill because of the bounty on his head, another player enters the scene.
Gamora (Zoe Saldana, Avatar, Star Trek) is after the strange sphere that Quill picked up. Gamora comes with a reputation of being a brutal killer, and while that is true, most people fear her because she is the adopted daughter of the titan Thanos. It seems that Thanos has made a deal with a rogue member of the Kree race known as Ronan (Lee Pace). If Ronan can provide Thanos with the sphere, then Thanos will destroy Ronan's enemy home world.
Unfortunately for Peter, Gamora, Rocket and Groot, the fight lands them all in prison where they meet the last member of their oddball band, Drax (Dave Bautista, known mainly from his WWE wrestling career). This massive man has a grudge to settle with Ronan, and he sees staying close to Gamora as a way to make sure he will get the chance to settle it.
Guardians of the Galaxy does a great job of not only standing on its own, but even indirectly helping to expand the Marvel Cinematic Universe. While very little of the film takes place on Earth, it gives a lot of hints about what appears to be brewing in the background of The Avengers story. Thanos, a character only hinted at before, is fairly prominently displayed. The idea of Infinity Stones is not only introduced, but expounded upon quite a bit (something that most Marvel comics readers are anxious to see played out), and we even get to see Benicio Del Toro's character, The Collector, developed some more since we only got a hint of him at the end of Thor: The Dark World.
Other supporting characters include Gamora's sister, Nebula (Karen Gillan) and Ronan's general Korath (Djimon Hounsou), as well as Glenn Close as the leader of the Nova people and John C. Reilly as one of her military personnel. While all four of these characters are a step below the Guardians or Ronan as far as importance, they serve their purposes in the story well. Both Nebula and Korath provided strong smaller antagonists, while Close played a good political leader and Reilly's character was a necessary bit of comedic relief when one of the main characters wasn't in a position to lighten the mood.
Guardians of the Galaxy also contains several featurettes, an audio commentary and a gag reel. The featurettes consists of a look at the visual effects behind the movie and an overview of the characters, sets and story. The third featurette is actually a bit of inside information for the upcoming Avengers: Age of Ultron film.
Guardians of the Galaxy is a must have for anyone building up their Marvel Cinematic Universe collection, but even outside of that overarching story, the film does an excellent job of standing on its own. Sure, having seen the other films will give you some extra insight, but when it comes down to the Guardians themselves and their particular story, you don't need to have seen any of the other films. Guardians of the Galaxy is a must see, at least.