In chapter 3. I paid attention to Nick's judgments. What do they reveal about his character that he does this? (refer to his opening comments).
I am assuming you are referring to Nick's comments about Gatsby's parties in your question. Notice the focus in these comments on the excess of the parties. The Rolls comes and goes from 9:00 am until after midnight. There are "eight servants including an extra gardner...toiling all day with mops....(43). Crates of oranges and lemons are delivered, and a juice extractor "could extract the juice of two hundred oranges...(43). An entire orchestra is hired to play, and cars are parked "five deep" (44).
Nick is from a "prominent, well-to-do" family from the mid-west (7). The habits and customs of such a family are never excessive, always being quiet and tasteful. Gatsby is shown as a representative of the nouveau riche, the "new rich," not from old money and a "good" family. As Nick observes Gatsby throwing his money around so loudly and excessively, I think he is simultaneously appalled and envious. You will notice that while he has a tone that suggests the whole party "scene" is overdone, he also seems to find beauty in some of the details.
After the detailed description of a Gatsby party, Nick goes on to explain that most of the people at these parties are not even invited. This is further evidence of Nick's quieter upbringing, in a family where only people who were one's friends would be coming to a party.
This notion of a midwestern understated superiority of old money and well-established family has been a part of the unspoken class system in the United States for a long time, and as Nick describes a Gatsby party, we can see him torn between distaste and admiration.