This is of course a massive question that you need to think through, and critics have differed on their opinions to this question since the first staging of this brilliant play. There is something tragic about the play and the way in which Nora and Torvald are forced to confront the reality of their lives and marriage and the way in which Nora has to admit she has been treated and kept like a doll for all of her life. This certainly is tragic, and we could also argue that her leaving this role and this house at the end of the play has definite elements of tragedy about it, especially when we consider the children that Nora is abandoning.
However, I find myself curiously uplifted whenever I consider the final act of the play. What drives Nora to leave her cloistered existence is the desire to finally live life for herself and to face it as an independent human being. Her desire to do this and to face the challenges of life head on and to discover who she is and to fashion her own role and identity in life, rather than have it fashioned for her, is something that I can't call a tragedy. In contrast, I think it represents something of the unvanquished nature of the human spirit that is determined to have the right to define itself rather than have others define it. Therefore, whilst there are elements of tragedy, I find the ending rather hopeful in lots of ways.