Fitzgerald is creating an ambience of affluence through the array of characters who are rich, temperamental, and, at times, condescending. By introducing the characters through Nick's eyes, Fitzgerald's strategy is to provide an outsider's perspective.
I would argue that Fitzgerald is creating the impression of an affluent society in which money talks and where fidelity and kindness don't seem to mean much. Tom and Myrtle's affair appears to be common knowledge, and Tom appears to be socially accepted in spite of his violent, arrogant nature.
The characters appear, at times, to be disrespectful and full of themselves. For example, Mr. McKee, who is introduced in chapter 2, shows his wife disrespect by cutting her off when she speaks. Mrs. McKee, for her part, is described as "handsome and horrible," giving a blunt description that could arguably be applied to many of these characters.
Tom becomes violent towards his mistress, hitting her hard enough to break her nose when she starts repeating Daisy's name. They live in a society governed by money and want for nothing. A classic example of this is when Myrtle "[sweeps] into the kitchen, implying that a dozen chefs [await] her orders there." Ultimately, I would argue that these characters—such as Daisy with her "sad and lovely" face—are proof that money does not buy happiness.
Before introducing his titular character, Gatsby, in person, Fitzgerald paints a picture of an opulent society governed by wealth and pleasure. By having the story told by Nick, who is a down-to-earth outsider, Fitzgerald paints a vivid picture of wealth and its impact on the various inhabitants of East and West Egg.
As mentioned, Nick is an outsider to the opulence and wealth, having acquired one of the few moderately priced rental properties in the area. His perspective is imbued with reflection and dry wit. As a man of limited means, he observes the wealth and decadence around him without being part of the lavish lifestyle.