Would you describe the atmosphere Fitzgerald is trying to convey as one of fulfilment, contentment, satisfaction, secret tension, dissatisfaction, or private anguish?
"The Great Gatsby" by F. Scott Fitzgerald.
Even when Fitzgerald presents characters who seem fulfilled (Tom, for example), he follows it with a juxtaposition of the opposite sentiment. In Chapter 1, we are introduced to Tom, Daisy, and Jordan who seem quite comfortable, content and satisfied. However, we quickly learn that Daisy is aware of Tom's affair with Myrtle Wilson, so she (Daisy) can not be fully content. The only people who seem genuinely content are Jordan, who is too laid back and liberated not to feel content, and Tom, who is too selfish not to feel content, what with a beautiful wife and a mistress on the side.
But as the novel is mostly about Gatsby, the mood seems to venture into the realms of fulfillment and contentment only as a tease. Gatsby's story, from Gatz to Gatsby, is about 'always already almost' having what he wants. And when he finally gets what he wants, it only lasts so long. And when he finally gets his dream (Daisy), he has built it up so much in his mind that there is a bit of a let-down. At the end of Chapter 5, Nick supposes:
There must have been moments even that afternoon when Daisy tumbled short of his dreams—not through her own fault, but because of the colossal vitality of his illusion.
After getting back together with Daisy, there is still the matter of winning her from Tom. In the end, she seems unwilling to leave Tom. Gatsby's story, up to and including his reunion with Daisy, is about secret tension, private anguish, and dissatisfaction or at least 'always already deferred' satisfaction. He is never fully happy. His story is comparable to George Wilson who probably had promise for his life at one time but now is left sifting through the 'valley of ashes' with his cheating, and then deceased, wife. The novel is often said to be about the elusiveness or the impossibility (without resorting to corruption and/or selfishness - Tom) of the American Dream. So, while there are moments of fulfillment, they are flawed, often achieved by devious means, and/or they are fleeting when achieved. The novel is about the lure of satisfaction and the teasing deferral of the American Dream.