Well Corey, since this thread seems miraculously to be still alive, I'll go ahead and fill in a gap or two myself.
Oh, it's fun!!
Janáček, Osud. Not as well known. I don't know why. There's some problem with different versions of the libretto or something. I don't remember things. Anyway, the music is sublimely seductive. I dare you not to love this opera!! (Just avoid Mackerras's Englished version. Not only is the English lame, but the performance is not up to Sir Charles generally lofty standards. There are two others, both in Czech, and they're different from each other but both good. I tend to favor František Jílek's. It was the first one I heard, and I prefer the soprano. But Albrecht's is superb. (Get both. It's only one CD.)
Prokofiev, Semyon Kotko. Wild and wildly beautiful. This is 1940 Prokofiev, at the top of his game.
Poulenc, Dialogues des Carmélites. Also tops. I usually don't pay that much attention to the story, but the ending of this won't let you ignore that element. (There's a moment in the Prokofiev that's like that, too. "Net net.")
Feldman, Neither. Pedants will assure you that this is not an opera. So shoot me. It's Feldman. It's great.
Nørgård, Nuit des Hommes. Good strong Nørgård. Makes me want his other, less readily available operas.
Kutavičius, Lokys, the Bear. Wildly addictive Lithuanian minimalism.
And (since I unfortunately do not know the Ashley operas) the pick of the opera crop, for me, Helmut Lachenmann's Das Mädchen mit den Schwefelhölzern. As good as Lachenmann gets, which means that it's as good an opera as it gets.
I'm sure I've left something really cool off this list, but it's late. Why am I still awake? Anyway, I'll add my voice to the chorus of Britten's Peter Grimes, which I saw three times when it was in L.A. a few years back. And Janáček's Katya Kabanova, which is so utterly gorgeous, I think I should listen to it now, just because I'm thinking about it. All Janáček's operas are good. Many of them are superb. And possibly the greatest opera of the twentieth century, Ligeti's Le Grand Macabre.
