The way this novel is written is similar to "Heart of Darkness" by Joseph Conrad in that it is one man's narrative about another man, one who is mysterious and draws others towards him. Gatsby and all the other characters are rather wasteful, idle people who continually gather for meaningless parties and other social meetings, none of whom, it turns out, are real friends.
The author does a good job of portraying this meaningless decadence and one-dimensional personalities of the age but this is perhaps the downfall of the book; creating unlikeable and one-dimensional characters to highlight disapproval for this type of person unltimately creates an unlikeable and one-dimensional story.
Whilst the language used here is of the times and both eloquent and politically incorrect by today's standards, the author matches the attitude of the characters with his writing style - skilfull indeed but when these people are rather languid and uninteresting this is not a great storytelling style to adopt in my opinion.
However, it is true that the messages in this tale are quite clear (money cannot buy everything, substance over appearances, don't live in the past) and as such this is more than just a story of the calamaties resulting from self-centred attitudes and there is an interesting, if rather brief, ending.
The Great Gatsby is a novel which has meaning and nice language but the style is rather dull in my opinion. It is recommended as an example of American literature, but the reader may find, like me, that this genre leaves them distinctly under-impressed. More the Rather-average Gatsby than Great.