O'Neill himself acknowledged thatThe Hairy Ape straddles a number of styles. "It seems to run the gamut from extreme naturalism to extreme expressionism—with more of the latter than the former," he wrote in 1921. The initial response to productions of The Hairy Ape focused on the skill of the play's staging and its forceful impact on a viewer. Describing O'Neill's skill with the voice of the working men, Alexander Woollcoot of the New York Times said, ''Squirm as you may, he holds you while you listen to the rumble of their discontent, and while you listen... it is true talk, all of it, and only those who have been so softly bred that they have never really heard the vulgate spoken in all its richness would venture to suggest that he has exaggerated it."

The playwright's intentions in depicting the world of the ship laborers was graphic: O'Neill intended the stokehole as a depiction of Hell. For Yank this isn't a problem. According to Richard Skinner in Eugene O 'Neill: A Poet's Quest, ''There is both splendor and terror at Yank's pride at being at the bottom." This pride, however, takes him through a number of episodes, culminating in the face-to-face meeting with a real hairy ape. In Yank's monologue directed to the gorilla, Skinner found "the most profound problem of the disjointed and divided soul." The critic continued, "Man is searching for peace in mere animal instinct and finding that then he can not throw off his manhood. The answer? Escape even from thought."

Although many dubbed it a challenging piece of theater, the majority of critics termed The Hairy Ape as a success. What the play is about, however, has been a topic of discussion. Some have claimed it is about the capitalist oppression of the masses (the workers), while others have termed it an examination of alienation in human society.

Alienation is a topic on which many critics have focused, the sense of dislocation that affects the firemen. Yank and his peers may believe themselves to be in touch with the world, better than the rich folks on the upper decks. The workers may echo Yank's sentiment that it is they who drive the world. But as Edwin Engel wrote in The Haunted Heroes of Eugene O'Neill, Yank enjoys "a false sense of belonging to something, of being part of steel and of machinery, whereas he is actually their slave." This enslavement is one that dawns on Yank slowly as he realizes he doesn't really belong anywhere.

The realization dawns with Mildred's visit to the stokehole. "Mildred has laid him bare," stated Thierry Dubost in Struggle, Defeat or Rebirth: Eugene O 'Neill's Vision of Humanity, ''He does not know where he fits into a world that has become incomprehensible to him, which is the reason for his wandering, his pathetic quest for community where he could be accepted and could at last be himself."

Although Yank was content in the secluded underworld of the stokehole, Mildred's visit shattered that insularity. After her appearance he starts referring to himself as the hairy ape. Despite Yank's tragic end, many critics have not viewed O'Neill's final message as one of permanent despair. '"The Hairy Ape' was to be only a symbol of the dark despair that sometimes sweeps over the soul to disappear later in a triumph of sheer will," stated Skinner.

Where does The Hairy Ape fit into the body of works that have prompted many to proclaim O'Neill as the most important American dramatist? O'Neill thought this play was very important, and it may be his most obvious exploration into how human beings are lost from their past and present. How they cope when any semblance of importance is removed from their lives. While The Hairy Ape is not considered in the same league as O'Neill's widely regarded masterpiece, Long Day's Journey into Night, it is noted as one of the playwright's more significant dramatic works and a highly effective example of expressionist theater.