Nick presents his favoritism for Midwestern values from the outset of his narrative. He dislikes the crass materialism of the ostentatiously wealthy. He dislikes the petty elitism and the dramas of the rich. He dislikes a lot of things about the world he chooses to live in for a while, in the east.
Yet, Nick comes to adore Jay Gatsby in a specific way. Gatsby maintains an innocence, despite his bootlegging and his lies. Gatsby remains a dreamer willing to pit fantasy against reality, fully believing that fantasy will win. These opinions come to play a significant role in the tenor of the novel's final half. Where Gatsby is raised up from the moil (which he has helped to create), Daisy, Tom and Jordan are all depicted as shallow and selfish people.
Nick does recognize the power of his own perceptions in shaping his story. When Tom attends one of Gatsby's parties, Nick finds himself viewing the scene through different eyes and recognizing how far he has come in creating his own version of things.
"It is invariably saddening to look through new eyes at things upon which you have expended your own powers of adjustment."
The quieter Gatsby (in comparison to Tom and Daisy) ends up seeming like the morally superior being, though this quietude is only a matter of bearing, not a matter of substance. Yet, this view is carried through to the end and Gatsby is allowed to remain associated with the midwest, while Daisy and Tom are made to bear the faults of the east.