In The Great Gatsby, how does Nick perceive Gatsby throughout the novel to conclude that Gatsby is "great"?

As the novel develops, Nick observes Gatsby and discovers
bits and pieces of the truth about his past, until all of it is eventually revealed.
Along the way, Nick is drawn into a personal relationship with Gatsby, who takes Nick
into his confidence and shares his deepest feelings. Nick's perceptions of Gatsby change
as he becomes deeply involved in Gatsby's life. When he first met Gatsby, Nick viewed
him as a larger-than-life presence in West Egg, a young man about his own age who
seemingly had "drifted" from nowhere into fabulous wealth. By the time Gatsby died, Nick
had come to perceive him as a romantic who had dedicated himself to an impossible
dream.

In Nick's estimation, what made Gatsby "great" was
not his enormous wealth or extravagant lifestyle, but the purity of his heart in
pursuing his "colossal dream" of loving Daisy. Gatsby was great in that his romantic
dream itself was great, to take control of life, repeat the past, and write a new fate
for himself. Since the novel is structured as a flashback, Nick introduces himself in
the beginning and makes his ultimate perception of Gatsby very
clear:

. . .
there was something gorgeous about him, some heightened sensitivity to the promises of
life . . . it was an extraordinary gift for hope, a romantic readiness such as I have
never found in any other person and which it is not likely I shall ever find
again.

Jay Gatsby, formerly
Jimmy Gatz of North Dakota, had come "a long way" and at the time of his death, "his
dream must have seemed so close that he could hardly fail to grasp it." For Nick, it was
Gatsby's formulation of that dream and his dedication to it that made him
great.