Walzzor makes a compelling point on this question, pointing out the performative nature of Gatsby's character. Gatsby is not only hiding his past from society (for the most part), he has also created a role for himself. The "monied man with manners and grace" might be one way to term the part he plays for society, covering his humble background.
Gatsby is not Gatsby but Jimmy Gatz, a poor boy from the Midwest—like Nick Carraway—who happened upon a chance that took him away from his life and gave him the opportunity to move into a different world.
The title of the novel then refers, to some extent, to the idea that "Gatsby" is a performed character - a show and a showman. He does not "belong" in the world of the wealthy elite and his outsider status is moral and social as well as historical. Yet, Gatsby poses as a person who does belong. So, in addition to Nick's astonishment at Gatsby's ability to dream and to pursue his dreams, Gatsby is also associated with the idea of playing a part.
Nick thinks Gatsby is great because he was able to create a new identity for himself when he needed to be someone else. Gatsby's determination and audacity are amazing to Nick. Gatsby focused on a goal, that of winning Daisy, and he did whatever was necessary to attain it.
Gatsby established that he would need wealth to keep Daisy in the manner she was accustomed to, and so he attained a "business" that would give him financial wealth. He studied mannerisms and expressions he thought would be what the social elite would say and do, and in this way , his gullibility is endearing.
Another aspect of Nick's admiration of Gatsby is the fact that he is a romantic at heart. Gatsby never veers from his goal and dream of winning Daisy, and even in the face of reality, his steadfast determination is admirable , if somewhat misguided.
Do readers end up feeling that Gatsby was really "great"? Or do they feel that he was a "hoodlum" who was just trying to be great in order to impress a woman? If the name Gatsby is false, then perhaps the adjective "great" is also false. Maybe Fitzgerald's title is intentionally ironic. Gatsby is a great pretender. Everything about him is false. He lies shamelessly. His mansion and his big yellow roadster are both symbols of pretense. Nick admired him and told him he was better than the others, but Nick did not consider him "great." In fact, he considered him rather naive and pathetic.
I would agree with renelane. Nick is a romantic, and while Gatsby's goal of "winning" Daisy could be the same as any competitor who wants to win, Nick attributes the cause to something more moral than materialistic. He says in Chapter 1 that when he left New York to return to the midwest, he had lost his belief that any human could be moral, with the exception of Gatsby. Now, Gatsby does many illegal things, but because he stays true to his emotions, Nick honors him.
Most of the relevant issues have already been covered above, so I'll just add that whatever faults Gatsby has, he's still more likeable than the other characters Nick observes. Though Gatsby's frequent use of "Old Sport" may be ingratiating, he's still free of the character faults so many other characters exhibit: greed, cynicism, bigotry, laziness, etc.
Nick's reason as for calling Gatsby "The Great Gatsby" may be for a number of reasons. One of them may be because of the amount of wealth that he possessed or that he acquired over time. This wealth, status, and fame are all worth noting in this novel. Another reason may be because of how Gatsby is on the inside. All Gatsby wanted was to be with Daisy, and for her he had risen up so he could be equal to her in terms of status. So that she would notice him and would return the feelings back to Gatsby. The answer to this question really depends on the reader's interpretation of the novel, the author's message, and the characters.
When you hear someone referred to as "the great Gatsby," you should immediately think of a magician. A magician both looks the part and acts the part, but in reality is not actually magic. I think that renelane hits a good point when she says Gatsby was "able to create a new identity for himself when he needed to be someone else." The illusion of Gatsby, created by Jimmy Gatz, is what makes him "great."
It seems to me that Nick is slightly obsessed with the idea of one individual being powerful, popular, and having everything they could ask for. I believe he personally would love to have some of the wonderful things Gatsby has, which is part of the reason why he puts Gatsby on a pedestal of amazement. Nick also has a great respect for Gatsby and all that he has achieved in his lifetime, despite his rocky childhood and young adult life.
I think Nick saw Gatsby as great because of the aurora he achieved and the way he achieved it. Although Gatsby was not from old money he made it seem like he was from old money. Something Nick thought was especially interesting. But what I think really got Nick is when he found out Gatsby wasn't really Gatsby and that he dealt with illegal things all in the name of love to get Daisy.
I think that Gatsby is essentially 'great' because in Nick's eyes all that he did was for a noble cause. He was a criminal and had lavish parties, reflecting the corrupt nature of the 1920s, but he did for love. Nick sees this as a noble enough reason. Also the last lines of the novel suggest that Nick was impressed by Gatsbys unwavering hope 'Gatsby beleived in the green light' - symbolising expectation, hope. You could also that the other characters have bad motives: Daisy is only having the affair with Gatsby for money, Myrtle as well for money, and Tom is just the bad guy - cheating on his wife because he can.
I don't think that Nick only believes Gatsby is great because of his perserverance in obtaining Daisy's love because it is not until mid way through the book that Nick even learns that Gatsby is seeking Daisy. There is something alluring about Gatsby from the very beginning..... but what? Nick is a hypocrite and claims to seek morality yet he dates the all too shallow Jordan, lies about his drinking habits and lives among the wealthy, while judging them the whole time.
I believe that Nick thought of Gatsby as great because of his unworldly love for Daisy. he took the blame for Daisy when she killed Myrtle, well at least he said he would, he never really got the chance seeing as how he died not long after.but the fact that he went through such great lenghts to attain what he thought daisy would want him to have so she would be with him, and promissing to cove for murder... that takes a great man.