So let's get this clear. The movie is not awful. It's not Battleship or some other Hasbro garbage. But is not a good movie for them and is one of my least favorites by them. I like the visuals, the jokes, and the acting. But there were some key story elements that did not happen. For example, there's a plot line that involves a dastardly act George Clooney's character did on his first Hollywood film. The act was revealed at the end of the movie in an offscreen conversation and written out quickly. Additionally a lot of the characters don't have purpose or a desire, other than create work for Josh Brolin's character Eddie Mannix.
Mannix is the protagonist of this twisty, seemingly meaningless comedy-drama. That description in itself shows how scattered the characters are. Huge stars like Ralph Fiennes, Tilda Swinton, and Scarlett Johansson pop in and out of the story with very little to do and loose ends that get tied up by a simple walk and talk with Eddie Mannix in the last five minutes.
The only actor who is given any other meaningful screen time is Alden Ehrenreich who gives a marvelous performance as country good ole boy Hobie Doyle. Hobie is a stud with horses but is brought into a adapted play directed by Ralph Fiennes' Lawrence Lawrence. The scene provides the only true moment of comedy of the whole film with an endearing Hobie and the artist Lawrence.
Now at the Q&A I learned about Hail, Caesar! before while it was shooting. This could be me only hearing what I wanted to hear but I could have sworn that Joel Coen said that Hail, Caesar! was going to be a musical.
It fits with the current cut of the movie. There are large musical interludes with Channing Tatum, Scarlett Johansson, and Alden Ehrenreich and music and old Hollywood is a big theme. Additionally the explanation of major off screen plot points through dialogue would make sense if these were originally supposed to be shown in a musical number. Channing Tatum's character is given a full length musical number and then has no dialogue until what seems to be the climactic scene. And this climactic scene has absolutely no context.
I think Hail, Caesar! was supposed to be in a musical and somewhere in the production that was cut. What was left was a hodge podge of actors, characters, and story lines tied together by Eddie Mannix and Roger Deakins.