I was biased against this movie to begin with, I found when reading it that the book was very overrated, though it had some interesting subtle metaphorical content, and was pretty eloquent, it these things have been done much better in books that also had good plot development, dynamic characters, complex philosophical questions, and were more engaging such as the book thief and dune. I did however, like the movie better in many ways. I found that it had good cinematography and scene layout, it tried to develop the characters more thoroughly (though in some cases it desperately failed, like with nick caraway), and it created certain motifs that were interesting and absent or limp in the book. Also, despite its differences it still managed to still managed to stick close to the original events and themes of the book. It did have faults however, for example, Spoiler Alert, well not really, it opens with this, Nick is telling the story from a sanitarium. This was unnecessary, and poorly developed, and just plain silly. Another issue is that one of the motifs, Gatsby's ring, was never metaphorically resonant, or meaningful. The biggest issue with this movie was that it was overdone, everything had to be profound or important or big, even when the subject wasn't big. I attribute this largely to the director trying to capture "The Great American Novel", this book is widely declared by critics to be one of the best ever written, and that puts a lot of pressure on an adapter, especially given that there isn't that great a story to work with in the first place.
Pros well paced, great actors, good scene developement, great cinematography
Cons overdone, mediocre story, sanitarium unnecessary and poorly developed