Oscar Isaac and Rachel Brosnahan revisit Lorraine Hansberry’s 1964 play on Broadway, following its sold-out run in Brooklyn.Lorraine Hansberry didn’t have the luxury of getting “The Sign in Sidney Brustein’s Window” right. In October 1964, days after the play opened on Broadway, a headline appeared in The New York Times: “Lorraine Hansberry Ill, Placed on Critical List.”She had been hospitalized before rehearsals started, but released in time to attend some of them. She saw previews; she attended opening night. Within two days, she was an inpatient again.A week later, another article: “Revisions Are Made in ‘Sidney Brustein,’” telling of “extensive script changes since its opening.”Then, on Jan. 13, 1965, a report of Hansberry’s death the previous day, from cancer, at age 34. “She was unable to help fashion the last play as it took shape in rehearsals,” the obituary read.All of which surely helps to explain the unwieldiness of “The Sign in Sidney Brustein’s Window,” a play that we might have looked back on as an early effort if only Hansberry had lived.Revised further by her ex-husband and literary executor, Robert Nemiroff, after her death, it has returned to Broadway, at the James Earl Jones Theater, with Oscar Isaac in the title role of a bloviating, early ’60s Greenwich Village intellectual. Rachel Brosnahan plays his wife, Iris, an actress manqué whose greatest feat of performance has been shaping herself into what he wants her to be.The leads’ considerable box-office appeal — Isaac perhaps most widely known for his role in the “Star Wars” sequels, Brosnahan for playing the title character in the Amazon series “The Marvelous Mrs. Maisel” — made Anne Kauffman’s production a scorching-hot ticket earlier this year at the Brooklyn Academy of Music. Rapidly transferring to Broadway, it opened last week on the final day of Tony Awards eligibility, while asking critics to stay away until this week. (I did not catch it in Brooklyn.)From left: Julian De Niro, Andy Grotelueschen, Brosnahan and Isaac as Village bohemians in Anne Kauffman’s production, a rare revival of Lorraine Hansberry’s play.Sara Krulwich/The New York TimesYet this seldom-seen play itself is a powerful draw. Clamorous with the voices of men, who take up an awful lot of oxygen, it is most incisive and piercing in the voices of its women, whom Hansberry draws with exquisite fullness. As a piece of theatrical and cultural history it is fascinating. And despite some sluggish moments, it does not feel overlong at two hours and 40 minutes, trimmed from three hours at BAM.The script’s unevenness does make you wonder, though, how Hansberry might have reworked it if she’d had the energy, and the privilege of time — and to what degree she, a Black woman and closeted lesbian in the very white, very male, ostensibly straight world of midcentury American theater, felt pressure to conform in her playmaking.Because really? Sidney Brustein, whom she has placed at the center of this crowded tragicomedy, is not an interesting person. This is not Isaac’s fault, although he ignores Hansberry’s stipulation that Sidney “laughs at himself as much as the world.” Isaac’s performance is mostly unremarkable but fine, sparking fully to life only in Sidney’s scenes with Iris’s wealthy, conventional sister, Mavis — the best role in the show, and the best played, by a thoroughly captivating Miriam Silverman. (The play is a Tony nominee for best revival; Silverman is its only acting nominee.)As written, Sidney is ridiculous, and stubbornly oblivious to that fact. Terrible at business, he has just bought a local newsweekly without mentioning it to Iris, because theirs is nowhere near a marriage of equals. The title nods to that: It’s Sidney’s window, not Iris’s too, even though it is in their living room. (The set, framed by girders reaching up toward the sky, is a suitably impressive Broadway debut from the design collective dots, lately omnipresent Off Broadway.)Sidney finds a smidgen of purpose when he agrees to back his politician friend Wally (Andy Grotelueschen), and puts a campaign sign in the window, advocating reform. Mostly, though, he is a man of thought, not action. Blusteringly self-important, he flails through life, naïve and directionless and pontificating nonetheless.“I know it’s hard for you, Iris, to understand what I’m all about,” he says near the top of the show, but already the audience has his number. The line gets a giant laugh.Iris, on the other hand, whom Sidney does not take seriously as an artist or an adult, knows exactly what her ambition is — and it no longer involves pretending to embody his particular pastoral romantic fantasy. Iris, imbued by Brosnahan with a fragile strength and perfect comic timing, works as a waitress while scheming to break into the theater.“I am 29,” she says, “and I want to begin to know that when I die more than ten or a hundred people will know the difference. I want to make it, Sid.”Brosnahan with Miriam Silverman, who plays Iris’s wealthy, conventional sister, Mavis.Sara Krulwich/The New York TimesIsaac with Gus Birney, who plays Iris’s younger sister, a baby-voiced Gloria.Sara Krulwich/The New York TimesIn a Hansberry play, it pays to keep your eye on the women. “A Raisin in the Sun” is as much about the female characters as it is about Walter Lee Younger. Similarly, you could shift the kaleidoscope just a bit and see “Sidney Brustein” as being principally about Iris and her sisters, Mavis and Gloria (a terrific Gus Birney, all baby-voiced dignity) — with a supporting role for young Alton (Julian De Niro), a rare Black character in this largely white play, who is in love with Gloria.The matronly Mavis, everyday elegant in delectable period style (costumes are by Brenda Abbandandolo), is bigoted, complicated and startlingly wise about life. Gloria, a call girl who tells Alton that she’s a model, is a sweet open wound. And Alton emerges as more injured and more furious than he’d let on.There are other characters here — David (Glenn Fitzgerald), a gay playwright neighbor, and Max (Raphael Nash Thompson), a painter-revolutionary — and a swirl of social forces: racism, misogyny and homophobia among them. But the three sisters and Alton are the soul of “Sidney Brustein,” the ones who make its ending land so potently. They exist inside a work that’s crammed with people and ideas in the way that first plays often are, before writers learn to take their time.Hansberry didn’t have time. If she had, I like to think that she’d have cracked “Sidney Brustein” open and done some recycling, making more plays about Iris and her sisters and their friend.The Sign in Sidney Brustein’s WindowThrough July 2 at the James Earl Jones Theater, Manhattan; thesignonbroadway.com. Running time: 2 hours 40 minutes. More