There's no doubt in my mind that was Snape. He always represented the great question in the whole series. What we needed was a justification for his acts and we finally had it. He was always good.

As for Kreacher, I thought that he changed too quickly and he was up to something. It turns out that he wasn't... good for him!

Dudley, well... he showed some decency, still a long way for redemption.

And Dumbledore... well, something about him had to come up. No one is 100% good, as some have pointed out. Dumbledore himself said that he has made mistakes and besides, he was devasted at his sister's funeral, to the point of not even defending himself when Aberforth hit him in the nose... and probably not even caring to mend it afterwards, being a great wizard, I am sure he could have fixed it perfectly. It was like he needed to leave some physical mark in himself to constantly remember him of his mistake... it was his own punishment to his behaviour. And, probably, his continuous belief in second chances was because he once needed one so badly.