Sasuke is a magnificently crafted character, very human and real. When one sees Sasuke and tries to put oneself in his shoes, one would realize that whatever he did, are all human-like responses; something most, if not all people given the power and opportunity, would end up doing. I love the fact that anyone's opinions do not matter to him. This is a sign of an extremely mature character, further strengthened by his resolve and his own created principles to look beyond the banners of Nations.
As we are talking about how good a character is and it's his verisimilitude that determines it so, then latest research expounds upon this factor that how people, who are stringent adherents of Religion, Patriotism, and such factors are not intellectually superior individuals, but in fact, it's the exact opposite. Being a character that opposed such confines from the beginning for his own views and perspectives on Life gives him a sense of Philosophical grandeur - he looks beyond boundaries and anyone who does so, is an intelligent and a thoughtful individual.
As for the Question, well Karin didn't recognize the chakra, honestly, god knows who it is. At first I thought it was Kabuto, now I am unsure. A mystery surviving Uchiha? Though I highly doubt it.