We can describe the atmosphere of this novel as "ironically romantic". The action and characters in the story are nearly all rather tawdry, morally speaking, yet yearn for the fulfillment of a dream. This notion is clearly applicable to Jay Gatsby, but it is also descriptive of Daisy, Myrtle and even Nick.
These characters foster hopes for the achievement of a particular dream. Gatbsy seeks an ideal future - one that includes wealth and Daisy, his first love. Daisy's dream includes the achievement of real, romantic love. Nick's romantic notions are expressed in his relationship with Jordan, wherein the two become engaged without ever really getting to know one another.
The irony of this romantic atmosphere is found in the failure of these characters to act in honesty. Driven by dreams, none of them truly engage with reality. Gatsby is willing to pay for his ideal by breaking up a marriage and, more literally pay through bootlegging liquor.
These characters have a poetic relationship with the visions they pursue. Gatsby's vision is especially poetic in its depiction, complete with a white ladder to the stars. This poetry is important and exists as an undercurrent of the entire novel, appearing poignantly at the novel's end.
Gatsby believed in the green light, the orgastic future that year by year recedes before us.… Tomorrow we will run faster, stretch out our arms farther.…
In these last lines, we see the meloncholy of ironic romance fully articulated. The dreams that inspires the poetry of the novel is connected to an unattainable future, equally unattainable as the dreamed of ideal past.
The dream of a future has its counterpart in a vision of a past state of innocence, which the characters seek in various ways and never find.