Coen brothers revisit the glamour and sometimes corrupt memories of Hollywood's golden age in the 50's. Josh Brolin plays the role of Eddie Mannix, a real-life fixer for studios. The movie also introduces Alden Ehrenreich, who seems to be a very promising actor... If Brolin is the heart of the film, Ehrenreich is the soul of it. The rest of the ensemble, although perfectly cast, have roles that are mostly glorified cameos.
The overarching theme of the movie is a film noir, and as mentioned, is a love-letter to the golden age. Coens show us a behind-the-scenes look at the movie making process. We basically see 3-4 films within Hail Caesar (from an epic historical sword and sandal, to a Gene Kelly-type musical). If you consider yourself a fan of film noir or the history of Hollywood, then you would thoroughly enjoy this movie. If not, then the disjointed story, number of cameos, and different movie genres within the film will confuse you. Of course this being a Coen brothers' film, you could expect to see lovable fools and eccentric characters. But I think this movie is rather polarizing.
Individual components of Hail Caesar are decent, but the whole package works surprisingly well. I give it 8.5/10.