Through the course of the series, Zuko is the character that underwent the most radical emotional changes. He started out as a typical Fire Nation prince, egocentric and commanding. After his banishment, his life was filled with hatred and longing towards capturing the Avatar, emotions that dictated all his decision-making. However, even when his goal was to capture the Avatar -which isn't a good goal on itself- his uncle managed to impart some of his wisdom and compassion onto Zuko. He had to face a lot of inner strive, but even when he was at his darkest, he still had a sense of honor over him, never totally succumbing to his darker side. When he then later decided to face his father and tell him that he was going to join the Avatar to teach him firebending, Zuko definitely left his darker days behind and officially became one of the good guys.
His last statement (a bit modified though) to the world also portrays his own journey he had made: the War had left him scarred and conflicted, but in the end, he managed to find himself and choose the right path, to help the Avatar. In the end, he announced that he would lead the world into and era of love and piece, with the Avatar's help.