Nick's attitude toward Gatsby is paradoxical: early in the novel he seems to frown at Gatsby's excess and lack of manners, but later in the novel he admires, even romanticizes, Gatsby as heroic.
This, of course, makes, Nick an unreliable narrator. Remember, the entire novel is told in flashback from Nick's home in the Midwest. Nick takes this opportunity to spin his tale in a certain light: one that makes him look more honest than he certainly is. He claims objectivity and restrained judgement, but the novel as a whole speaks otherwise: he is as subjective and judgmental about Gatsby as Tom is about the white race.
Nick virtually equates himself with Gatsby: they are tied at the hip. Critics have read the novel in a homosexual perspective; I see it more as a Jesus / Nicodemus relationship. Gatsby is the "Son of God" to Nick's converted follower. Just at Jesus invited the Pharisee to seek rebirth in baptism, so too does Gatsby elicit Nick's re-conception of the American Dream. In short, Gatsby's romantic ideal of himself has rubbed off on Nick by the end of the novel to the point of cult hero worship. Gatsby is Nick's Byronic Hero. Gatsby's desires are so focused that Nick becomes jealous of them, to the point that they share the same desire: Daisy. Nick is complicit with Gatsby in trying to attain her.
Gatsby's excessive desires and beliefs in the American Dream are what make him great...and what lead to his tragedy. Only in America can one re-invent oneself the way Gatsby does, and this fascinates Nick. Nick sympathizes with the proletariat working-class, and he respects Gatsby for having leaped across to the bourgeoisie and still kept his boyish, humble ideals.
Very few personalities in world history, like Alexander the great, have the title 'the great' appended to their name. It's obvious that the sobriquet 'the great' is used ironically by F. Scott Fitzgerald to hint at Gatsby's dubious and corrupt personality and actually highlight the failure of his dream in attaining Daisy, and overall Gatsby's insignificance .
This is evident when we compare and contrast Ch. 3 and Ch. 9. In Ch.3 we have the lavish description of the spectacular parties thrown by Jay Gatsby in order to attract Daisy:
Every Friday five crates of oranges and lemons arrived from a fruiterer in New York—every Monday these same oranges and lemons left his back door in a pyramid of pulpless halves. There was a machine in the kitchen which could extract the juice of two hundred oranges in half an hour if a little button was pressed two hundred times by a butler’s thumb.
At least once a fortnight a corps of caterers came down with several hundred feet of canvas and enough colored lights to make a Christmas tree of Gatsby’s enormous garden. On buffet tables, garnished with glistening hors-d’oeuvre, spiced baked hams crowded against salads of harlequin designs and pastry pigs and turkeys bewitched to a dark gold. In the main hall a bar with a real brass rail was set up, and stocked with gins and liquors and with cordials so long forgotten that most of his female guests were too young to know one from another.
In Ch.9 we have a description of Gatsby's funeral and the now desolate house. The character Owl-eyes sums up the striking contrast between the splendor of Gatsby's house in Ch.3 and the deserted look in Ch. 9:
We straggled down quickly through the rain to the cars. Owl-eyes spoke to me by the gate.
“I couldn’t get to the house,” he remarked.
“Neither could anybody else.”
“Go on!” He started. “Why, my God! they used to go there by the hundreds.” He took off his glasses and wiped them again, outside and in.
“The poor son-of-a-bitch,” he said.
At the end of the novel Nick takes one last look at Gatsby's house and remarks:
On the last night, with my trunk packed and my car sold to the grocer, I went over and looked at that huge incoherent failure of a house once more.