Today marks the 163th anniversary of the birth of Friedrich Nietzsche, philosopher extraordinaire and (who knew?) opera buff. He had definite opinions: Bizet, good; Wagner, bad. Of course, being a philosopher, he was a little more wordy than that. As quoted in his entry in Grove, the music in Carmen "is wicked, cunning, fatalistic: it remains at the same time popular ... It is rich. It is precise. It constructs, organizes, finishes." On the other hand, "Wagner's art is sick." Yikes.
If you've a hankering for the wicked and cunning, here's Callas as Carmen. Sick art more your thing? How about a little Walküre with Kirsten Flagstad? Or read something by the man himself.