First, the title has nothing to do with the movie, except that George Clooney is in a Roman centurion costume the whole time, which does nothing for him. He looks rather fat and is getting old. Not a good look for him.
Second, I like old movies, so I got a kick out of the in-jokes and references to Esther Williams, Carol Reid, Gary Cooper, etc.
Third, I think the film can be taken two ways: as a satire about communism and supposed communists in Hollywood (they were such dilettantes who really didn't understand or mean it) or a poke at the stupidity of the American people for buying into the "crap" that Hollywood puts out so cynically. And yet the main character, Mannix, believes in what he is doing and is able to look past the sins of his "clients" to keep creating the dreams. The replication of scenes with just a tweak of "modern winking" is fun, although a little sad, too. For example, the sailors singing about missing "the dames" and then dancing is a perfect homage to Gene Kelly (very well staged), but ends up as a recognition of the dancers' unrecognized homosexuality.
The final scene where Clooney, who is supposed to be the centurion at the cross, gives a speech about who Christ is, and everyone on the set is very moved, and then he forgets his line and curses, is the key scene. Hollywood creates something that resonates with us, that stirs us, but the reality underneath is nonreality, all pose, all pretend.
However, I thought the scene where the Catholic priest, Orthodox priest, rabbi, and Protestant minister discuss the script of the Biblical epic to be priceless and not really offensive, though I imagine some would.
So, this is a Coen brothers' movie, and most people don't go to those unless they are already "into" Coen brothers' movies, and it isn't as good as Oh Brother Where Art Thou because what made that great is the music, and it isn't anywhere near Fargo or No Country for Old Men, but those are hard to watch. What I do find interesting in both of those two is that the unstoppable male killers are countered, either successfully or unsuccessfully, by a woman. In NCFOM, although she is killed by the nemesis character, the wife who finally tells the killer off at the end is the voice of reason. There are of course a lot of other movies they made. I sort of put them in the Woody Allen category. You go to the films because of who makes them, not for entertainment per se, and maybe entertainment will result. In the case of Hail Caesar (add punctuation), entertainment ensued for me but I doubt it would for most.