This remarkable autobiographical play is generally considered to be O'Neill's finest work, and he himself believed that the last scene was the best he had ever written. It is a play of little outward action but a great deal of interaction of past and present, in terms of the lives of four members of this intertwined family which cannot forget. It observes the Aristotelian unities scrupulously and has refined dramatic action to a minimum, being an orchestration of confessional and self-exculpatory monologues interspersed with familial interactions. The autobiographical elements are clear, and for that reason O'Neill restricted its release, refusing to allow it to be printed or played until twenty-five years after his death when all the participants would be dead. But he reckoned without Carlotta Monterey, his third wife who insisted on its release. Later, Karl Ragnar Gierow, director of the Royal Dramatic Theatre of Stockholm, with the assistance of the then secretary of the United Nations, Dag Hammarskjold, managed to obtain per-mission for its presentation in Stockholm, where it was a resounding success. A New York production followed shortly after, and the play has since been ranked as possibly the greatest naturalistic American drama to date, winning O'Neill, posthumously, a fourth Pulitzer Prize.

In this drama, O'Neill resurrects and exorcises old ghosts, coming to terms with his father but not with his mother, for whom he shows some sympathy but never forgiveness or understanding. Jamie [James O'Neill, Jr.] is celebrated in A Moon for the Misbegotten while Long Day's Journey belongs primarily to the playwright's father James O'Neill, with O'Neill's own exculpation of him-self in the character of Edmund. The tale of his tuberculosis in 1912 is true, as was his father's original intent to send him to the state farm. In fact, O'Neill actually did spend a little time there before transferring to Gaylord Farm, the locus of The Straw. The accounts of O'Neill's sea travels and attempted suicide are also true, but O'Neill is easy on himself as Edmund, for he edits out the fact of his first marriage and first son, as well as the help his father gave him to leave the country. The circumstances of Mary Tyrone's addiction are also identical to those of Ella Quinlan O'Neill, including the death of a child from measles, though O'Neill omits her breaking of the habit. But the play is more than mere autobiography because it shows the struggle of human beings in torment, and at times O'Neill assesses things with the greatest clarity, especially his own poetic talent. In general, he did just "stammer," though he had the feelings and intellect of a poet; but in this play, he reaches greater heights than elsewhere, partly because of his intense emotional involvement. The setting, in Monte Cristo Cottage, New London, goes beyond either realism or naturalism because this little world encapsulated in fog becomes symbolic of the human condition and the traps in which human beings find themselves caught, without possibility of release, because they are so disoriented by fog that they have lost their bearings, both psychological and spiritual—a metaphor for loss of faith, for unfulfilled ambitions, for wasted lives which end in death without ever having celebrated life but continually avoided it whether through liquor or morphine. Only Edmund seems to have the possibility of escape, though in this play it is tenuous. Long Day's Journey also has affinities with the earlier Ah, Wilderness! which might be termed the comic view of O'Neill's family life in New London and which has also gained considerable popularity. The later play, however, is by far the greater achievement both emotionally and dramatically. Here O'Neill has come to trust his actors, giving each one of them a chance to shine, for every part requires a professional of great ability, even star quality, for the success of a production.