Unlike other Marvel Cinematic Universe films, this one contains very few references to the other titles in the series. Amongst the few that are present are the brief appearance of Thanos (who was teased in the The Avengers (2012) end credit scene), and the Tesseract/Cosmic Cube clearly visible as one of the Infinity Gems the Collector describes.
According to James Gunn, Ronan's ship the Dark Aster is designed after a mausoleum: "It's minimal and brutal, a stark gray colorless world devoid of any set dressing whatsoever, and relying purely on its heavy concrete-like architecture to convey its tone and function."
Some audience members misheard a line late in the movie, leading them to believe it was a goof. Peter Quill actually states "they got my dick message", referencing a previous scene, and not "they got my text message".
At the Kyln, when the Guardians are dealing with the Monstrous Inmate, Gamora is behind Quill when she speaks. When it cuts to a wide shot, and all the shots that follow, Gamora has disappeared. We don't see her leave.
The main villain will be Ronan (Lee Pace). Nebula (Karen Gillan) and Korath (Djimon Hounsou) will be secondary villains who serve Ronan. The Collector (Benicio Del Toro) and Thanos (Josh Brolin) also make minor appearances but pose no direct threat to the Guardians. Since the character Yondu (Michael Rooker) serves as a foil to the main protagonist Peter Quill/Star-Lord, he can be considered a minor antagonist. In this film, Collector, while cruel to his slave, is not a villain, but rather serves as a buyer for the Infinity Stone.
Was this Thanos' first screen appearnace?
No, he previously appeared during the closing credits of The Avengers, where he was played by stuntman Damion Poitier.
Where is Stan Lee's cameo in this movie?
Stan Lee is seen on the planet Xandar. Rocket spots him with a younger woman and berates him for cheating on his wife. He laughs and calls him a Pervert.