There are so many genres of opera. There are the exquisite chamber operas that are close to plays like Strauss’ "Capriccio" of Gluck’s chamber operas. There are the operas of morality or ideology like Beethoven’s "Fidelio" or Mozart’s "Idomeneo." Some works highlight verismos raw emotions and atonal expressionism, decadent excesses like Berg’s "Lulu" or the opera of scandal, like "Salome" and the late romantic opera as epic poetry, "The Ring." The list goes on and on.
Few, if any, operas can bear comparison with the gestation, preparation and final execution of Giuseppe Verdi’s "Un Ballo in Maschera." It is the work that definitively closes his middle period; preceded by "Traviata,""Rigoletto," and "Il Trovatore" and followed by his supreme masterworks "Don Carlo," "Aida," "Otello" and "Falstaff."
There are essentially two versions of Don Carlo for Giuseppe Verdi. I don't mean that one is in French and the other Italian. Historians and musicologist are manic about the fact that this is untrue; however, there is a work, Don Carlos (francophone's are insistent on this), originally written in French for the Paris Opera that was so vast (5 hrs and change, they say), and it's richness so prodigal, that it obscured the works greatness.