As for me one of the main treasuries of the book is the wonderful, highly artistic  language. It was sometimes even hard to read a chapter, but the wish to learn what will happen always prevailed. As it was mentioned, that the author was very close with Hemingway and now, reading "Farewell to arms", I see  why. Both Fitzgerald and Hemingway were keen on being famous, and they both  had one feature - to be unique, be the one for his readers, be different from others. But they managed to do it bu using different approaches:  Hemingway made up his mind to use simple language, but his forte was swirling plot and the enormous amount of  events. Fitzgerald prefered to win attention by the beauty of the language, showing his own already formed style. 

Another thing that should be mentioned is the importance of using SYMBOLS in the novel. In my book it is written that "The Great Gatsby" is a psychologic novel. So now it is important to make it clear why it is considered like this.