I think Nora is a character who is defined by the slamming of the door behind her as she walks away from her marriage, her children and her comfortable life with Torvald. There is much to admire about her character and actions. In particular, note the reason why she leaves everything, as she says in Act III:
I have been performing tricks for you, Torvald. That’s how I’ve survived. You wanted it like that. You and Papa have done me a great wrong. It’s because of you I’ve made nothing of my life.
Nora bravely faces the truth that she has not really been living her own life and instead has been living a life that the men in her life have wanted her to lead. This of course results in the powerful metaphor of the doll's house, with Nora as the doll. She has been kept as a little girl. What is so noble about Nora's actions is that she is determined to change this and is willing to take the massive risk of going out there by herself and living her own life so that she can find herself and mature.
At the same time, however, there is something very shocking about Nora's actions, particularly in the way that she leaves her children behind as she embarks on her search for self. It has led Ibsen's play to be judged rather harshly, as some conclude this is the selfish action of a mother that will impact her children negatively. Nora flouts all social codes and customs by rejecting her role of wife and mother. However, on the other hand, we could argue that this is precisely Ibsen's point. Nora's action is so dramatic because it emphasises just how constraining the position that society has created for women is.