Aristotle implicitly holds it up as the great example of a tragedy. "Imitates life" does not mean it is "realism," but rather that it does not rely on supernatural outs. The fates are obviously supernatural in our minds, but not for the Greeks. It certainly is a serious story - though what he means is that it deals with kings and not clowns, and is one worthy of contemplation. This is a kingly story with great implications about fate and free will. And the play most certainly evokes this pity and fear, especially when you know what's coming. Oedipus declares almost at the beginning that whoever is at the root of this problem will be destroyed - once we, as the Greeks would have, know that it's he himself who is the cause, then the rest of the play is watching him destroy himself by pursuing the truth so nobly.