In The Great Gatsby, Gatsby represents several things to Nick, and Nick's feelings and thoughts about Gatsby are complex.
Nick says at one point that Gatsby is everything he hates. Financially, Gatsby is the corrupted American dream. His partner fixed the World Series--messed with America's past time.
Romantically, Gatsby is naive and foolish. He's spent five years constructing his persona and life in such a way as to lure Daisy back to him, hoping to recapture a relationship that never really was.
Yet, Gatsby is also an attractive character to Nick. Gatsby's love was "pure" and all-consuming. Gatsby loves like everybody should love. And Daisy would have been better off with Gatsby.
By the end of the novel, Nick makes Gatsby's funeral arrangements, hunts down people to try to get them to attend the funeral, takes care of Gatsby's father when he arrives at the house, and, significantly, tells Gatsby he is worth far more than all of "them," worth far more than everybody else in the novel. Gatsby was special.