There are a number of different aspects of Fitzgerald's style in this novel that are worthy of attention. I think one of the most interesting is the way that Fitzgerald combines a huge number of different forms in his narration alongside an omniscient narrator to tell his tale. Consider for example the occurrence of letters, notes, lists and the dramatic form that is utilised to depict the start and the finish of Rosalind and Armory's relationship. This novel therefore is not simply a linear narrative told by one narrator.
We can analyse this stylistic element by thinking about how modernist authors found the traditional novel form with its linear narrative too restrictive for their purposes. Fitzgerald here is playing with a number of different ways of presenting information that clearly points towards a more creative approach.
Secondly, we can also say that the mish-mash of such different narrative forms and mediums is rather disruptive for the reader. However, this disruption and rather chaotic feel to the text as a result of the different mediums helps the reader to capture something of the raw reality of the characters and events in the novel that a smoother, and more unrealistic, linear narrative would enable the reader to do.