Throughout the novel, we see evidence that Nick is quite judgmental about practically everyone he meets and even more so about his favourite person, Jay Gatsby. In the opening pages, he has this to say about Gatsby:
Gatsby, who represented everything for which I have an unaffected scorn. If personality is an unbroken series of successful gestures, then there was something gorgeous about him, some heightened sensitivity to the promises of life, as if he were related to one of those intricate machines that register earthquakes ten thousand miles away.
It is clear that Nick admired Gatsby tremendously and practically placed him on a pedestal. He ignored all indications that Jay was involved in criminal activity and maintained a positive view of him throughout. This perspective, however, is not true of his judgment of others.
He clearly despises Tom Buchanan for example, and uses negative terms when he refers to him, as he for instance does in chapter one when he mentions:
He had changed since his New Haven years. Now he was a sturdy straw-haired man of thirty with a rather hard mouth and a supercilious manner. Two shining arrogant eyes had established dominance over his face and gave him the appearance of always leaning aggressively forward. Not even the effeminate swank of his riding clothes could hide the enormous power of that body ...
There is a clear contrast between Nick's opinions of the two men. In his eyes, one was heroic and the other an arrogant villain. This judgment is extended to others whom Nick felt were exploiting Jay's grand generosity and innate goodness, such as the guests at his party. Nick refers to most of these people in derogatory terms, mocking them:
But I can still read the gray names, ...
From East Egg, then, came the Chester Beckers and the Leeches ...
.. and a whole clan named Blackbuck, who always gathered in a corner and flipped up their noses like goats at whosoever came near.
And so he continues. Nick clearly found these characters despicable and he makes no attempt to hide his disdain for them. Even those with whom he has close personal contact, do not escape his criticism such as the people he met in Tom Buchanan's apartment. Of Catherine, Myrtle's sister, he comments:
... the efforts of nature toward the restoration of the old alignment gave a blurred air to her face.
Mr. McKee was a pale, feminine man from the flat below.
His wife was shrill, languid, handsome, and horrible.
In his final meeting with Jay Gatsby, Nick sums up his sentiments when he tells Jay:
“They’re a rotten crowd,” ... “You’re worth the whole damn bunch put together.”
Clearly, this should not be the opinion of a man who claims, at the beginning of the novel:
... I’m inclined to reserve all judgments,
It is obvious that Nick has forgotten the advice that his father had given him:
“Whenever you feel like criticizing any one,” he told me, “just remember that all the people in this world haven’t had the advantages that you’ve had.”
Nick, therefore, for all his claims of 'reserving judgments' and being 'one of the few honest people that I have ever known' comes across as quite hypocritical and superficial in his perception of others. He has not once reserved judgment and comes across as quite the opposite, after all. He, in fact, comes across as quite self-righteous and somewhat supercilious.