In A Raisin in the Sun there are some moments where characters act cruelly and maliciously toward one another, but these moments pass, and by the end of the play the family is reconciled. Other than some comic teasing, they are all on the same side, united in meeting the challenges before them, however difficult those might be.
The Sign in Sidney Brustein's Window has a much more uncompromising vision. All of the characters are unpleasant, and the married couple at the heart of the play are so nasty to one another that not only are we not sure if they will end up together, but we don't even know for sure if we want their marriage to survive. In this production, Sidney is played by movie star Oscar Isaac, while his wife Iris is portrayed by television actress Rachel Brosnahan. Both are famous for playing flawed characters on screen, which works well for the play.
Instead of portraying working-class characters like in Raisin, Hansberry chose in this work to analyze the (mostly white) hipster bohemians of Greenwich Village. Though this group of outsiders should support one another, they instead pick at each other, making cringe-worthy comments that can contain the most offensive of slurs. At a disastrous dinner party, a Black man and a gay man exchange insults until they both walk off in anger. As a queer woman of color, Hansberry likely understood the harm various kinds of hate can cause, but she chose to expose the flaws of characters who should have been allies.
To me, the most interesting character was Iris's sister Mavis, played by Miriam Silverman. Though Mavis appears to the Village bohemians to be a "square" and a "sellout" for marrying a wealthy businessman and moving to a house in the suburbs, we learn that she has known suffering they've never seen. As soon as we start to sympathize with Mavis, however, Hansberry allows her to slip out a piece of casual racism or anti-Semitism that will make us fume and roll our eyes. This is a play where everyone is a victim and everyone is a perpetrator.
This production originated at the Brooklyn Academy of Music before transferring to Broadway. It's running only until July 2nd, so if you want to catch it, go now. You might not get another chance to see this show on Broadway for a very long time.