In the March 22nd New York Review of Books, Charles Rosen reviewing the current production of Verdi’s Ernani at the Metropolitan Opera:
It is clear that Verdi was planting his flag in the field of the most extreme Romanticism (though Ernani, admittedly, is not as silly as the next great opera of Verdi, Il Trovatore, where the gypsy Azucena tries to avenge her mother’s death by kidnapping the baby brother of the Count di Luna, whose father has ordered her mother burned at the stake; she intends to throw the baby into the still smoldering fire, and somewhat absentmindedly throws her own baby in by mistake).
Rosen’s synopsis of the libretto of Ernani is just as funny, but longer.
Opera libretti are a rich field of weirdness. Mozart’s (well, Schikaneder’s) Magic Flute is notoriously hard to summarize in a way that makes it sound sensible. Anna Russell made a career out of retelling Wagner’s Ring Cycle for laughs. And so on. Some libretti merely have small tinges of oddity: Puccini’s Manon Lescaut set in “a desert outside New Orleans”, for example.
Maybe someone has already assembled a collection of Amazing Libretti in synopsis. (I’m reminded of a collection of Amazing Torts put together, in newsletter form, by Harvard Law School friends of mine many years ago.)