Fitzgerald proves that he is good...good at creating a world, good at introducing characters, good at giving glimpses of how complex they are...and also, good at ending the story. At first, it seems rushed. You spend so much time finding out little things about Gatsby, that when he enters the stage, you just want him to stay. Gatsby starts not like the man, but the mith. Everybody seems to know the missing piece of information about him, and, yet, most of them haven't even met him.
In the last chapters, it feels wrong: Gatsby is no longer extraordinary, is no longer above the others. So, if at first, it feels like he is the prototype of a stuggling man fighting to achieve pure happiness, he becomes an average man, trying in vain to win over Daisy, the woman who has lost all belief in true love, the common woman. Everything starts feeling cheap, overrated, so the ending comes at the right time.
Although the book starts by giving the impression that will tell the story that broke the boundaries, it ends up opening the eyes at the mediocrity of the world. so this is what makes the book worthy: the way it shows you that you spent too much time building a dream, and not enough pursuing it.