To me, Creon is a rather weak man who has been thrust into a position of authority and is afraid he won't be able to handle it. As a result, he doesn't dare reconsider any of his decisions--doing so, he thonks, might make him appear weak and cause his subjects to lose respect for him. So when he orders that Polyneices be left unburied and then orders Antigone to be entombed alive when she's caught violating the order, he can't let himself listen to her or Ismene (mere girls) or to Haemon (sons don't tell their fathers what to do). He even refuses to listen to Teiresias, conveying the displeasure of the gods, until Teiresias has left, but in fact that message offers him a face-saving way out, Surely no one can call him weak for backing down in the face of divine displeasure. Even then, however, he makes the same mistake Teiresias has accused him of: getting things backwards. Teiresias points out that he has buried the living and left the dead unburied, and now, when the chorus advises him to free Antigone and bury Polyneices, he does those two things in reverse order, so that Antigone is left in the tomb to despair while Polyneices is being given a royal funeral, and she hangs herself. At the end, after her suicide has led to that of Haemon and his to that of his mother, Creon must face the fact that his misguided stubbornness has destroyed his personal world.
So,in a nutshell, what's his tragic flaw? In Greek tragedy, it's usually hubris--excessive pride. In Creon's case, that pride takes the form of being afraid to admit that he has made a mistake; and, as usual, it leads to his downfall and drags innocent people down with him.
