Act IV of Hamlet is structured differently from Acts I-III in several ways.
Firstly, Act IV is much shorter than the preceding acts, with only five scenes compared to the fifteen scenes in Acts I-III. This makes Act IV feel more condensed and focused, with a tighter narrative arc.
Secondly, Act IV is largely set in a different location than the previous acts. While the earlier acts take place primarily in and around the castle in Elsinore, Act IV mostly takes place in a prison in Denmark.
Finally, Act IV contains some of the most intense and dramatic scenes in the play, including Hamlet's confrontation with Rosencrantz and Guildenstern, his encounter with the Norwegian army, and the tragic deaths of Ophelia and Laertes.
The structure of Act IV, with its shorter length and focus on intense, dramatic scenes, creates a sense of urgency and heightened tension. The audience is drawn into the action and may feel a sense of unease or foreboding as events unfold. Additionally, the shift to the prison setting and the focus on the tragic consequences of the characters' actions contribute to a somber and melancholic mood.
Overall, the structure of Act IV serves to intensify the emotional impact of the play's tragic events and heighten the audience's engagement with the story.