Gatsby was "great," and he was tragic. It isn't clear to me what made Gatsby “great.” He had money (lots and lots and lots of it); he was not a hypocrite like his antagonist, the man who had married Daisy, the woman Gatsby loved; he had class. What did Gatsby know besides how to get rich? He knew he loved Daisy, but he thought he knew more than he did: he thought he could overcome absolutely any obstacle with his love of Daisy, and hers of him.
He fought in WWI. Certainly the trenches were not where the life was free. It seems Gatsby had more than one thing in common with the Austrian-born philosopher, Ludwig Wittgenstein, who was a decorated war hero!
Wittgenstein was born into wealth; Gatsby achieved it. Wittgenstein gave his huge fortune away. Gatsby lost his only when he died. Wittgenstein wrote a key philosophical tract in the cataract of mustard gas and machine-gun barrages. Gatsby wrote one of the most famous love letters in US history under the same circumstances.
Wittgenstein died of prostate cancer; Gatsby died with a bullet through his heart, both literal and metaphorical. Cupid was not a sympathetic character in Ovid's “Metamorphoses.”
A life with Daisy was still a possibility at the moment of Gatsby's death, as far as we know; and Wittgenstein probably would have known the modal logic of it. Maybe Gatsby ran up against the laws of the world: the fates will intervene to prevent time travel, to prevent bringing the future back, into the past, and the past into the future, the way Gatsby wanted to do.
In the midst of avarice, hypocrisy, sin and riches, he remained a good man; but what made him great? It was not his hope; I can't see how hope is in and of itself great. His sources of wealth may have been questionable; the bootlegging certainly showed the hypocrisy of his nemesis, Buchanan, Daisy's husband and “the polo player.” Gatsby “went to Oxford” the way I “went to” two well-known universities; and neither of us claims to be “a Such-and-such man,” implying we are the products of a full education there. When pressed, he admitted this about himself. He was forced into honesty. He lost his temper, nearly punching Buchanan in the face; but would Buchanan have pushed Daisy out of the window, beside which she and Gatsby were standing, if she had said she'd never loved him?
What was the importance of her saying she never loved him, anyway? It was required, by Gatsby, so their five-year separation would not be tainted by time's passage. Nothing happened during those five years: that was something Gatsby needed to know to believe one could relive the past. Gatsby insisted it be done; everything must go according to his plan, or it would not be perfect, and so would be nothing. It was not enough for the present to be what it was: the past must have been the present and vice versa.
Gatsby's last word was: “Daisy!” Wittgenstein's were, "Tell them I've had a wonderful life." Which had the greater achievement: Gatsby, who loved Daisy but perhaps perfection more; or Wittgenstein, who loved philosophy but perhaps perfection more? I see Wittgenstein's achievements through a glass darkly, and in the end it seems his life and love of philosophical perfection were enough for him. I see Gatsby's hope outrunning the possible as quixotic desperation, not altogether a bad thing.
Near the end of hope, and in the midst of catastrophe, with Daisy's automobiling encounter with Buchanan's mistress having just occurred, Gatsby flexes his plan, and is willing to run away with Daisy. If he had just run away with her when she told him she wished they could do it – but Gatsby's obsessiveness led to his rigidity, and if it wasn't perfect, it was not acceptable to him; he insisted on his own way, even to his and Daisy's ultimate detriment. It was his tragic flaw, his seeking of perfection and of the world's going according to his plan up to the last and smallest detail. At one point he makes a gesture with a finger, of a straight, diagonally ascending line in the air. "My life must be like this," he says. He didn't know about "what [success] really looks like."
The relentless drive and single-mindedness that allowed him to become “The Great” Gatsby was his undoing. He and Daisy could have run away a number of times. But love wasn't enough for Gatsby.