Nick is somewhat annoying as he is an unreliable narrator who vacillates in his opionions and morality. He, too, is somewhat deluded in his self-perception as he considers himself outside the parameters of the amoral others; however, he is at times intrigued by this lifestyle and suffers some internal conflicts as a result.
Nick tells the story in a way that is, in one sense, unrealistic, but which is very satisfying.
The unrealistic elements of the narration grow out of Nick's telling of Gatsby's story. Yes, we are given a context that explains how Nick knows what he knows about Gatsby's past, yet this context is essentially a thinly veiled slight-of-hand on the part of Fitzgerald.
Beyond the formal oddity of using Nick as Gatsby's mouthpiece for extended space in the novel, I find Nick to be a thoroughly intriguing narrator.
He learns quite a bit and is sarcastic and intelligent enough to both let the reader know how much he is learning and to play down the importance of his epiphanies.
I like Nick as a narrator because he confesses upfront that he has been trusted by many. Then, he confesses that one man had the fortune of escaping Nick's moral compass, and that man was Gatsby. I like when someone can be upfront and just deal with their own problem. Nick knows he's judgmental and admits it.