Impressionistic authors normally create an emotional landscape of types. This being said, the emotional landscape in The Great Gatsby is most definitely NOT a happy one. The descriptor elegiac is certainly apt. The question however, is whether or not Nick Carraway fits the mournful role.
Nick Carraway claims to be one of the only honest people he's ever met in the novel. He also refers to his relationship with his father quite a bit. His father constantly encouraged him not to judge others. Nick seems to be honest and seems to be a kind hearted person, however, he is constantly judging others (calling Daisy careless, pg. 9). Nick came from a fairly simple life out west. This more complex life startles him and causes him to become bitter toward the fast paced life. He begins to lose himself amongst the drive for "purpose" and "importance". Nick's personal character is not elegiac, however the Nick he develops into during the course of the novel is certainly elegiac.