A Doll's House is realistic in many ways. It is realistic in the choice of subject matter. It is realistic that the doctor has a sexually transmitted disease. It is realistic in the fact that there is no happy ending—that Nora walks out. However, in some ways, it is not so realistic. The timing of everything is a bit too easy, and the social scene in which the Helmers operate seems overly small and precise, like, well, a doll house.
As a play of social reformation, it is limited, but all the more realistic for being so. It limits the proposed reform to the actions of a single woman, Nora, and doesn't solve all the problems. Instead, she takes a single action: she rejects the social structures she's lived in, and leaves, literally and figuratively. That's what makes this play useful today, when more developed suggestions for social reform have faded.