Before I move on, I shall note that the book is always better. And I don't mean that this is a bad movie - on the contrary, I did enjoy it, but if you really want to fully grasp the essence of The Great Gatsby, go for the book.
For anyone who hadn't read the thousand of reviews published already, the story is set in 1922 during the Roaring Twenties, and tells the story of the mysterious and incredibly rich Jay Gatsby who organizes larger-than-life parties in an effort to meet again with the love of his life, Daisy. Daisy in the meantime, while she used to be in love with Gatsby before the war, when Gatsby had to leave for his army service, she got married to Tom Buchanan, one of richest men in America. The story is told through the eyes of Nick Carraway, a cousin of Daisy's, who unlike any human being I know, reserves all judgement throughout the book, despite all the upheaval taking place between the characters.
It is said to be Fitzgerald's magnum opus, quite possibly the Great American Novel, and my favourite book - and that's a quite a statement considering I've been a bookworm all my life.
In other words, read it.
Now, if you're already a classic literature aficionado, I'm afraid you'll have to scale down your expectations for this film. Although essential points in the book like the character of Jordan Baker or the relationship between Myrtle and Tom are hardly explored, I do appreciate that the film was made with the wider audience in mind.
Not everyone wants to think about the highlighted contrast between old money and new money. Or whether The Great Gatsby is the Great American Novel. Or whether Daisy is a victim or not.
Some people just want to watch the movie, enjoy all the glitz and glamour and decadence of the Roaring Twenties (which were portrayed quite well I must say), and then go home. I suppose the film was made for these people, so if you haven't read the book, you'll still enjoy the film.
On a more positive note, I liked that Nick was presented as an alcoholic in a sanatorium. Although on-screen he appears a bit boring and hollow, and as the narrator he does not judge any of the characters, not even rogue and dumber-than-a-sac-of-rocks Tom, he was still a (dramatic) construct of his time.
Also, the costumes, oh the costumes, were what they should have been, impressive, flamboyant and all that Jazz-age (got it?). Carey Mulligan as Daisy was careless, coy and childish with some momentary flashes of true emotion - quite probably the kind of Daisy Fitzgerald had envisioned. DiCaprio was probably like Gatsby would be if he wasn't fictional: mysterious, powerful but insecure, hopeful but delusional.
Also, the music was quite fitting of the film with a range artists from Beyonce and Jay-Z to Lana Del Ray and Emeli Sande lending their voices for the film soundtrack.
All in all, I recommend you watch it, but if you've studied the Fitzgerald novel before, do scale down your expectations.