In my mind, I think that one of the most critical elements for Aristotelian tragedy is the idea of reversal in characterization. This idea suggests that real tragedy is where characters travel far in understanding their own failures. Aristotle feels that there has to be a point where characters recognize that their own failures caused their own tragic predicament. This sense of the "pathetic" and something that resembles a "catharsis" is essential in Aristotle's conception of tragedy.
This is not seen in Antigone. The way she is at the start of the drama is how she is at the end of it. She doesn't change and there is little in way of acceptance of her own role in her own tragedy. When she talks to Ismene or Haemon, there is little in way of acknowledgement or little in way of acceptance of her own failures in her own condition. She does not die in the manner that shows personal pain, but rather dies in a manner of defiance and dissent from start to finish. I think that Creon does a better job of fulfilling this condition of Aristotle's notion of tragedy, as he recognizes the role of his own stubbornness as a part of his tragic condition.