Why is Nick Carraway an interesting narrator?

F. Scott Fitzgerald chose to write The Great Gatsby with a fictitious narrator named Nick Carraway. Nick introduces himself at the very beginning of the first chapter:
In my younger and more vulnerable years my father gave me some advice that I've been turning over in my mind ever since. "Whenever you feel like criticizing any one," he told me, "just remember that all the people in the world haven't had the advantages that you've had."
Nick represents himself as an exceptionally broad-minded, tolerant person. His creator must have felt that this characterization of his minor-character narrator was essential because Nick could be accused of questionable, if not immoral, behavior. He makes friends with a gangster named Gatsby, who throws riotous parties fueled with bootleg liquor.
Nick is the sole connecting link between all the other principal characters. He is related to Daisy and related to her husband Tom through her. At the same time, Tom introduces Nick to his mistress Myrtle Wilson, whose husband George has no idea what Myrtle is up to when she goes into Manhattan supposedly to visit her sister. Nick is the only character besides Tom and Myrtle who knows about the love nest Tom keeps for Myrtle in the city. Nick is the only one except Gatsby and Daisy who knows about the affair they are having in Gatsby's mansion. There are two adulterous affairs going on simultaneously, and Nick gets personally involved with all the parties involved. He justifies this to himself by telling the reader that
In consequence [of what his father told him] 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 holds all the threads in his hands. He tries to represent himself as being somehow above it all; he retreats to the Midwest to get away. In the end he makes everybody look pretty bad, except for himself and his friend Gatsby. Daisy is guilty of manslaughter. Tom is guilty of adultery, along with Myrtle, Daisy, and Gatsby. George Wilson is guilty of murder. But Nick Carraway is not guiltless either. He is deceiving Daisy about Tom's affair and deceiving Tom about Daisy's affair. He is indirectly helping to deceive George Wilson about Myrtle's affair. He participates in the cover-up of Daisy's hit-and-run manslaughter. Nick thinks he is being tolerant and broad-minded, but perhaps he is letting himself be morally tainted by unscrupulous and dissolute people, including Gatsby himself. Nick seems like a character hypnotized by his admiration of a strong, handsome, highly determined, self-made man and drawn into a whirlpool of corruption.