In The Great Gatsby, we have a(n):
Unreliable narrator: Nick claims to follow his father's advice and be impartial, but he is clearly in Gatsby's corner throughout. He falls for Gatsby's dreams and ignores his shady past. Nick even hosts the date with Daisy, and he is the only one who attends his funeral. As such, we see Gatsby as the hero through Nick's eyes.
Highly ornate literary style: Nick narrates using much color imagery, socio-economic and moral symbolism, and direct and indirect characterization. Really, this is Fitzgerald's voice coming through Nick. This style stands in sharp contrast to the minimalistic and understated style a Hemingway speaker, for example, would narrate the story.
Observer-Participant Narrative Style: Nick is primarily an observer and critic of human action. He is rarely the main character in his own narrative. He is a fly-on-the-wall, a guest at the the parties, not the host or festive party-goer. Although not detached, Nick certainly distances himself from the established rich like the Buchanans.
Flashback / Memory Tale: Remember, Nick is narrating the entire novel from his home in the Midwest after Gatsby's death. Nick bases the whole narration on memory and the passage of time. Just as Gatsby tried to recreate the past with Daisy, so too does Nick try to recreate the past through Gatsby.
Middle-West and Middle-Class Slant: Nick, like Fitzgerald, is from the heartland, and he is critical of the Easter rich. He calls them "careless." So, his socio-economic values are of the middle-class and from the Midwest: certainly more modest than the outspoken New Yorkers.