comparison with the original story (spoilers)
I read "The Glass Key" a few weeks ago, and while there are a number of changes with the plot and characters, the movie is a reasonable adaptation.
I thought the entire sequence of beatings by Jeff was overdone in the movie; but I went back to the text and it happened just like that, including Beaumont (Ned in the book, not Ed) setting fire to a mattress and then waking up in the hospital.
The violence in the movie was far more graphic. In the book, Jeff said how much he enjoyed beating guys up, and especially Beaumont. But the beating was not described, only how Beaumont felt when he regained consciousness. And there was no sadomasochistic sexual undertone in the book, though Jeff accused Beaumont of being a "massacrist".
I don't think Alan Ladd was any great actor, but he played Beaumont very close to the character in the book. Same way with the other main characters, like Varna (O'Rory in the book) and Janet Henry, Paul Madvig, Farr the DA, and so on.
An insignificant detail, but ultimately important. Senator Henry argued with his son, they scuffled, the senator took Paul's walking stick and killed his son with it -- then returned home and left the monogrammed stick by the door in its usual place. This was the clue that suggested the Senator was the killer -- how did the murder weapon get back inside the house? In the book Paul was seen arguing with Taylor Henry on the street, but Paul was not present when Taylor was killed, though he returned while the Senator was standing over his son's body. In the movie the explanation how Beaumont figured it out was much weaker, IMO.