For some reason I had never seen this version of "The Great Gatsby"; having recently read the novel, I thought I might finally watch it.
My main impressions were that (1) the screenplay follows Fitzgerald's novel more closely than most screen adaptations of books and (2) on the other hand, the effect of the story gets blurred behind a fog, that is: the production of this movie as a sort of "roaring twenties epic" rather than the more intimate, people-focused feel of the novel. The film has outstanding production values: cinematography, sets, wardrobe - but rather than just serve as a tool to recreate the 1920s, they became a goal in itself, as if the director was thinking something like, "it would be a shame not to use our budget to its fullest" or "let's give the folks who might find the story too boring something gorgeous to look at".
As for the cast: I thought the main actors were very good, and that the cast gave good portrayals of the characters, with one exception, Bruce Dern as Tom Buchanan. It is not that his acting was bad, on the contrary: I think he was miscast as Tom, and his interpretation of what Tom was like was all wrong. In the novel, Tom Buchanan is a more natural, straightforward kind of brute, as summarized by Nick, the narrator, as he concludes that he could not remain angry at Tom since he was like a child. Bruce Dern plays Tom as a more self-aware kind of con man. In the novel, at the end (no spoilers), I could believe Tom's sincerety as he expresses his feelings; in the film, he sounds like a hypocrite.
Many people have criticized the casting of Mia Farrow as Daisy. I thought she was an excellent choice. Granted, she may not correspond precisely to how Daisy is described in the novel. But she conveys the character's shallowness, with feelings that are fickle but nevertheless genuine, and which can plausibly charm those, like Gatsby, who mistake her present-moment, circumstancial feelings for something more durable and profound. The contrast between Daisy's personality with the more intelligent and perceptive Jordan, well played by Lois Chiles, is immediate and very true to the book.
As for Robert Redford as Jay Gatsby: my expectations sunk when I saw how the film changed the scene where Nick is introduced to Gatsby: from a casual encounter in the middle of the party, as in the book, to a mysterious, "James Bond villain" meeting in the film. Maybe the director felt it necessary to do that because the book scene would not work on screen, since viewers would immediately recognize Redford. But in any case, I thought that after that scene, Redford's portrayal of Gatsby was very good and mostly true to the book.
Overall, I recommend this film; but, maybe ironically, I think it might have been a truer portrayal of Fitzgerald's novel if it had been made with a smaller budget.