It is important to realise what a landmark this play represents in dramatic history. Prior to the opening of this play, the audience of the nineteenth century went to see a play to be taken away from their world and to see marvels and romance. The expectation was that they would be treated to somewhat contrived and sensational stories of love affairs and lost heirs, not anything remotely resembling their own hum-drum existence. Ibsen therefore dramatically altered these expectations with this play.
In this play, therefore, we are presented with all the tragedy of a real life situation that the audience could definitely relate to. Ibsen treated the stage as if it were actually a room, and the way actors moved on stage was intended to look real, rather than posed or affected. Also, the dialogue employed reflects the realism of the play. His characters use colloquial speech that make them seem credible individuals. Interestingly, Ibsen was one of the first playwrights to incorporate stage directions that would help the actors convey a certain feeling to the audience.
For all of these reasons, especially considering what came before, this play is said to be one of the first "realist" plays that changed the future of drama forever.