Nick is the narrator in The Great Gatsby. If it wasn't for Nick, we wouldn't have the background information on Gatsby we get in Chapter 6, and this is of vital importance because it shows his progression from James Gatz to Jay Gatsby. 

Nick is also a very reliable narrator. Despite the fact that he is a character in the novel, he is able to maintain a relatively objective perspective on the events of the novel. In fact, he prides himself (without seeming too proud or pretentious) on this fact. At the beginning of the novel, he notes this quality, one that indirectly comes from the lessons of his father: 

In consequence, I’m inclined to reserve all judgments, a habit that has opened up many curious natures to me and also made me the victim of not a few veteran bores. 

Nick is therefore not judgmental in the pejorative sense. Nick does make judgments but they are relatively unbiased. He examines particular things such as the nuances of Gatsby's and Daisy's gestures. He recognizes symbolic features in some of the other characters' (namely Gatsby's) lives. For example, Nick notices that when Gatsby and Daisy are reunited, the beckoning green light at the end of her dock has lost, for Gatsby, its symbolic significance. 

Compared to the great distance that had separated him from Daisy it had seemed very near to her, almost touching her. It had seemed as close as a star to the moon. Now it was again a green light on a dock. 

Throughout the novel, green becomes symbolic of Daisy, the American Dream, and money. Nick subtly points these symbols out and in this way, he acts like the reader's guide as he deciphers the other characters' behaviors, revealing their motivations and desires. 

What is Nick's role in a conflict in The Great Gatsby?

I would classify the main conflict of this novel as one of character versus society; Nick, the protagonist, conflicts with society, represented by people like Tom and Daisy Buchanan, and even Jordan Baker, as a result of their selfishness and "carelessness." They are rich and, therefore, have the privilege of being able to smash "up things and creatures and then [retreat] back into their money or their vast carelessness, or whatever it was that kept them together and let other people clean up the mess they had made." And though Nick does seem to harbor some romantic feelings for Jordan, even in the end after all the drama between Tom and Gatsby, he ultimately cannot enter into a truly committed relationship with Jordan because of his misgivings about her. These individuals, representative of society's values, are deceptive, materialistic, and selfish, and Nick conflicts with them as a result.

What is Nick like as a narrator in The Great Gatsby?

Nick is a first-person objective narrator. This means that he is a participant in the story's events and uses the first-person pronoun "I"; he also is telling the events of the story after they have taken place (rather than during). He knows how everything ends, even before he begins telling the story, and so this colors his telling. He knows that Gatsby dies, and he knows what kind of people Tom and Daisy really are. This knowledge biases him against the Buchanans. He may claim to refrain from judgment, and perhaps he does hold back as many of these events take place, but their ultimate conclusion could only encourage his judgment of certain individuals. In chapter 1, he says that

Only Gatsby, the man who gives his name to this book, was exempt from my reaction—Gatsby, who represented everything for which I have an unaffected scorn . . . Gatsby turned out all right at the end

Nick is not unbiased then. How could he be? After witnessing the cruelty of Tom and Daisy, after witnessing the odd brand of innocence possessed by Gatsby—the inherent optimism of a man who believes he can reclaim the past and turn back time—how could Nick not judge?

What is Nick like as a narrator in The Great Gatsby?

The Great Gatsby is told from the perspective of Nick Carraway, who is what readers would call a peripheral narrator.  As the word 'peripheral' suggests, this kind of narrator is on the outside looking in toward the main action of the story.  As a peripheral narrator, Nick is not the center attention, nor is he the protagonist of the story; instead Nick comes to West Egg and acts as an observer to all of the action between Gatsby and the Buchanans.  Nick informs the reader from the very beginning in the first chapter that he is "inclined to reserve judgment" which makes him, for the most part, a fairly unbiased narrator.