This is, as other reviewers have pointed out, one of the few gangster pictures of the early '30's to focus on law enforcement rather than the gangsters. Although sympathetic law enforcement figures were often supporting characters in such films (e.g. Thomas Jackson as Sgt. Flaherty in LITTLE CAESAR, C. Henry Gordon as Sgt. Guarino in SCARFACE, Clark Gable as reporter-turned-undercover-DA's-investigator Carl Luckner in THE SECRET SIX, or an uncredited Robert Homans as a nondescript beat cop in THE PUBLIC ENEMY), they were not the focus of the films; the charismatic mobsters were.
Novelist W.R. Burnett, who wrote the novel on which LITTLE CAESAR was based, and who adapted Armitage Trail's novel SCARFACE into the Paul Muni film, was, probably more than anyone else, responsible for the popularity of the gangster figure in films. He was one of the co-writers of the screenplay for BEAST OF THE CITY, and is also credited for the original story.
But, it wasn't really an original screen story. Burnett's second published novel, SAINT JOHNSON (1930), was the first fictionalization of the face-off between the forces of the law, represented by the Earp brothers, and the forces of criminality, represented by the Clanton gang, in Tombstone, AZ. The reality was at least a little more nuanced, but in general, the Earps really were the good guys, to the degree anyone was, and the Clantons really the bad guys. Certainly, though presenting the characters warts and all, that's the depiction Burnett gave in his novel, and his fictionalized Earp figure, Wayt Johnson, is, though deeply flawed, principled and heroic.
What Burnett did in BEAST OF THE CITY was, essentially, to adapt SAINT JOHNSON for the screen, substituting Depression/Prohibition-era Chicago for 1880's Tombstone, a similarly upright, but modern-day urban police chief for his Earp figure, and a fictionalized Capone mob for the fictionalized Clanton gang.
Coincidentally, mere weeks after Paramount released this contemporary version of SAINT JOHNSON, Universal released LAW AND ORDER, a more faithful, western version of the novel, with a script by John Huston (who would later both adapt and direct the film version of Burnett's THE ASPHALT JUNGLE). Even more coincidentally, the Earp-based law officer in this version was also portrayed by Walter Huston.
Burnett's work seemed particularly suited to this sort of cross-genre adaptation. Just as he turned his western novel into a contemporary police film, his gangster novel, HIGH SIERRA, filmed with Humphrey Bogart as the gangster Roy Earle, would be remade as a western, COLORADO TERRITORY, starring Joel McCrea, and THE ASPHALT JUNGLE, starring Sterling Hayden, would be remade as a western, THE BADLANDERS, starring Alan Ladd.
It's interesting to compare BEAST OF THE CITY with LAW AND ORDER, but, on balance, I have to say that BEAST OF THE CITY is a better cop film than LAW AND ORDER is a western. Huston's performance in both is crisp and professional, and he was that rare actor who could move back and forth from leading roles to character roles.
Jean Harlow is very good, and it is, as others have said, a tragedy that she died so young. It seems as if she was Marilyn Monroe before Marilyn was.
Wallace Ford is okay, but not great, as Detective Fitzpatrick, Chief Fitzpatrick's unreliable younger brother, but better than Luther Hopkins was in the counterpart role in LAW AND ORDER.
The biggest disappointment (and really, it's not that big a disappointment) is Jean Hersholt as Sam Belmonte, the Capone figure. He's pretty good, but compared to Paul Muni's verson of a fictionalized Capone in SCARFACE, or even Wallace Beery's in THE SECRET SIX, Hersholt is lacklustre. Plus his kindly image, forged in his later films and TV series as "Dr. Christian," works against his being accepted as a ruthless mob chieftain.
All in all, though, if it's not quite in the same class as SCARFACE (the best of the "Gangster Big Three" of the early '30's), it's at least a technically better made film (coming a little later, and taking advantage of technological advances) than either LITTLE CAESAR or THE PUBLIC ENEMY.