Gatsby is first described in the opening chapter of The Great Gatsby. Nick, the novel's narrator, implies that the story he is about to narrate retrospectively made him lose his faith in people. He says that the only person in the story who didn't make him lose faith was Gatsby. Gatsby, he says, was "exempt from [his] reaction."
Initially, Nick tells us that Gatsby "represented everything for which [he has]an unaffected scorn." Earlier in the chapter, Nick tells us that he dislikes insincerity and dishonesty, so we can thus assume that when Nick first met Gatsby he took Gatsby to be insincere and dishonest. However, Nick then says that there was "something gorgeous about [Gatsby]." He elaborates and says that this "something" was a "heightened sensitivity to the promises of life." From this we might infer that although Nick initially did not like Gatsby, he later came to admire him for his willingness to embrace life.
The warm tone of admiration in this first description of Gatsby continues when we are told that Gatsby had "an extraordinary gift for hope, a romantic readiness" that Nick has "never found in any other person." The tone of this description is one of approval and admiration. Nick seems to admire Gatsby for his optimistic attitude towards life.
Later in the same passage of the text, Nick describes Gatsby as a victim. He says that it is "what preyed on Gatsby" that made him lose his faith in people. He further describes a "foul dust" that he says followed in Gatsby's wake, suggesting that Gatsby was perhaps the victim of this "dust." The tone of these later descriptions is sympathetic and somewhat sober.