Do the characters seem like real people?

Yes, the main characters in the novel seem like real people. They are both sympathetic and flawed, as real people are. Nobody is a cardboard cut-out hero or villain, not even Tom Buchanan.
Nick is level-headed, sensitive, and a lyrical writer with a gift for being able to sympathize with Gatsby's tragic grandeur. But his flaw is that he lacks self-knowledge. For example, he talks about how he is deceiving a girl back home by not breaking off their relationship even though he is getting increasingly involved with Jordan Baker. Nevertheless, after revealing this, he states that one of his "cardinal" virtues is his honesty. (A good rule of thumb: any character who insists on his honesty probably isn't completely honest). Nick might think he is honest, but he is clearly capable of deception. 
Daisy is beautiful, charming, and unhappy. She draws men to her, but she is also selfish and spoiled. Tom is the villain of the piece, a racist womanizer who lacks a poetic streak, but we feel for him when he realizes that everyone around him has deceived him about his wife's affair with Gatsby.
Jordan is a pleasing but elusive figure, who may or may not cheat at golf. Myrtle treats her husband badly but is sympathetic because of her yearning to have a better life than the one offered her in the Valley of Ashes.