Nietzsche is a cynic and a critic, at best. He is not one to praise anyone or anything lightly, but in The Birth of Tragedy, Nietzsche just can't help himself. Never before in any human art, or any time afterward, have humans conceived of artistic experiences as original and true as the Greek tragedians. That's Nietzsche's opinion, at least, and he unravels his opinion through these essays, ultimately explaining the function Greek tragedy played in the formation of an educated public.
See, in Greek tragedies, the hero's enlightenment is not optional. Because of the passion and fervor the Dionysians brought to the theater experience (they were all likely very drunk, for instance), the Greek tragedies were able to become very grand in scope, to the point that sometimes the plays were experienced like religious myths. And, because the theater itself provided a structure that made people actually pay attention, everyone witnesses the same thing at the same time, meaning that the effect of the play is multiplied again through the group psychology of the audience. The effect is that narrative became a sort of religious experience, the effect of which was to disturb and unnerve those who were prideful in their estimation of life.
To be prideful for Nietzsche would be something like this: A person who does not fear the unknown, who believes that life's biggest questions just "work themselves out" or something, that person would be prideful, because life is so full of suffering and chaos that even the best, strongest, wisest of us cannot escape life without failing in some major way. To Nietzsche, that was the value of tragedy, and it was for that purpose that the form was born.
