Dr. Jekyll and Mr. Hyde is an emotionally charged film. Fredric March plays Henry Jekyll, a physician who has it all: he's born into wealth; engaged to the beautiful Muriel Carew (Rose Hobart); he tends to the poor, and is beloved by his patients. But you know the story: Jekyll is overconfident that he understands human nature, develops a concoction to separate and distill the good and evil natures in each person, but the concoction leads him to be consumed by his Hyde persona. March is convincing as Jekyll who is at turns kind, impetuous, arrogant, and penitent. But he is really fun to watch as the cackling, sneering, brutal Hyde. The actresses who play the "good Jekyll woman" (Hobart as Carew) and the "bad Hyde woman" (Miriam Hopkins as a working-class prostitute) really make the film work though, because it is how Jekyll/Hyde inflict pain on the women he loves that really drives home the tragedy of the film. I felt touched by Hopkins' performance--her character lusts after the good Jekyll but she is brutalized by Hyde and she realizes too late that rescue by Jekyll is not possible.
The film is marred by occassional scenes that come off a bit corny and florid to a 21st century audience. I also thought that Mamoulian's extensive use of subjective photography, especially in the opening scene--verged on being gimmicky and ostentatious.
A couple of other things noteworthy about the film: It was pretty racy for its time. Namely, the scene where Hopkins lays in bed with Jekyll in her apartment and it is strongly implied she striped naked to seduce him.
One of the most powerful scenes I thought was where Jekyll goes to his fiancee to "set her free", as he does so, the enormity of what he's done dawns on him. This is a man starring into the abyss.