I really just wanted this to be a bit funnier than it was.
It's not a bad movie, but I think perhaps it tried to stuff in more than it should.
The overarching story is of Eddie Mannix (Josh Brolin), who is a movie studio fixer in the 1950s. That is, his job is to keep the stars in line and make sure all the PR is good. He arranges for this and that star to be seen together, covers up when someone is in rehab, etc. He traffics in stress, and goes to confession daily. There's an almost throwaway subplot of his being offered another, less stressful and better paying job by Lockheed Martin, but [spoiler] of course he turns it down. He says his work "feels right." Which, being religious, he takes to mean God wants him to continue doing it.
Unfortunately, I didn't feel much empathy or sympathy for Eddie, and since a lot of the movie rests on the viewer necessarily connecting with him . . . It fell flat for me. I only found myself thinking he was stupid for not taking the Lockheed job so he could spend more time with his family. It's hard to be sympathetic toward someone so selfish, no matter what reason he thinks he has. His studio family needs him more? Pfft.
Eddie is the connective tissue, then, for a variety of story lines that include one star (George Clooney) being kidnapped by Communists, another (Scarlett Johansson) trying to hide a pregnancy because she's unmarried, and a Western star (Alden Ehrenreich) taking a turn in a drama while also being set up on a date with a fellow star in the name of PR. His was the cutest story arc, certainly, and Ralph Fiennes does a nice turn as the director of the drama struggling against Ehrenreich's thick accent. Even so, it's not enough to save Hail, Caesar! from feeling lackluster. The setting and time period are definitely worthy, the stories told here not so much.
At the end of the day, Hail, Caesar! is less than the sum of its parts.