The critical response to This Is Our Youth has been overwhelmingly positive. Many critics, like Robert Brustein, in his review for the New Republic, have applauded the play's realism and praised Lonergan as a "penetrating cultural historian." Brustein characterizes the play as a "sharp [x-ray] of social abscess and moral atrophy," noting its "tough-minded, almost clinical examination of the aimlessness, the vacuity, and the emotional deadness" of its privileged main characters. He concludes, "Lonergan's capacity to evoke these qualities without moralizing about them is the mark of a significant writer."
Stefan Kanfer, in a review for the New Leader, echoes Brustein's assessment of Lonergan's talent when he writes, "A lesser playwright might have been content to let [the initial conflict] occupy the evening." But while Dennis and Warren are trying to decide what to do about the money, "Lonergan introduces a third party and takes the play to another level." Kanfer insists that "the star of the evening is the playwright, who summons up a world much larger than the three actors onstage" and who has "a gift for character analysis, dramatic tension and the kind of wry, ironic dialogue that jump-starts the Off-Broadway season."
In his review for Variety, Matt Wolf claims that Lonergan is "a playwright blessed with an ear so finely attuned to slacker-speak that every 'um' and 'man' seemed to encapsulate an era." Wolf comments that this "master dramatist" "clearly and cleanly sets forth" the play's "jumble of emotions." He notes "how seamlessly orchestrated the play feels, its landscape encompassing burgeoning romance and long-abiding friendship alongside sudden and brutal ache." In a closing note, he praises the "numerous perceptions so piercingly captured by a play that could not seem more adult."
Richard Ouzounian, in his review for Variety, has a darker vision of the play, concluding that it is "a deeply disturbing look at the moral emptiness of a generation." However, in her review for American Theatre, Pamela Renner calls it an "acerbic comedy" and says that "the transitional self of adolescence is hard to pin down in writing, but Youth draws urgency and propulsive strength from its presence."