Iversen wrote:And as gsbod rightly mentions I do give a subjective account, but apart from my preference for instrumental music and dislike of serial music I will mostly discuss music that I also like myself.
Speaking of operas, there are comprehensive instrumental versions of several Puccini operas (search for "Kostelanetz") plus at least four very long instrumental excerpts from Wagner's Ring cyklus on Youtube, and there are ouvertures and balletmusic galore from the whole long history of opera - but when you consider how much time many composers have wasted on opera and what they could have written instead then it is a tragedy. Take for instance Schubert: his Rosamunde music has been recorded, but he wrote at least 16 other operas, which even opera buffs don't never ever hear because their libretti were so totally ridiculous. OK, most opera libretti are ridiculous, but from what I have read on the internet it seems that those used by Schubert were in a class of their own. Or take Mussorgsky and Borodin who both died before they could finish their operas. If they had spent their time on something less voluminous than fullsize operas then we could have had a mountain of valuable original works by these two persons - now Rimsky-Korsakov and Glazunov had to spend their time on finishing those operas from scraps and/or memory, and the number of instrumental works by both Mussorgsky and Borodin can be counted on a couple of hands for each of them ...
As someone who prefers instrumental music, who didn't like choral music for most of their life (annnd then I joined a choir and realized how amazing choral music can be), and who rarely watches or listens to opera I think that saying that someone has wasted time writing an opera is subjective at best (which I realize you foregrounded) but also just not useful or helpful. I mean Bruckner also wrote very
long symphonies, just think of how many more he could have written had he kept the bulk of them under an hour. Amusingly I just found a new compilation of Decca
recording of Bruckner's symphonies 1-9 by the Vienna Philharmonic on Naxos' website. Never mind the sheer number
that Schubert wrote. I haven't listened to any of his operas, but it's not as if he was unable to spend his time churning out pieces that are still popular.
Borodin also just didn't compose a large number of pieces in general all things considered and Mussorgsky wrote 48 instrumental pieces (if I counted correctly - I'm including his works for piano of course) and a number of vocal pieces that weren't operas. I think that there is something to someone who is explicitly trying to learn about classical music listening to to the original versions of pieces if at all possible, perhaps paired with a different commonly performed arrangement. So the original version of Mussorgsky's Pictures at an Exhibition and then the symphonic version, which is despite the fact that I prefer the symphonic version.
I get wishing that composers who have long died had composed different pieces than they did, really I do. Given how amazing the flute parts are in multiple symphonies that Shostakovich wrote, I wish that he had written a flute concerto or sonata. While Prokofiev did write a flute sonata, it was only the one. That's despite his amazing (and absurdly difficult in some cases) flute parts in his symphonic works. That said all of this wishing is not worth spending a lot of time and energy one. I can't change the past and I certainly can't influence composers who died before I was born. My options are to arrange an existing piece for flute or to accept that what I wish had happened hadn't happened and realize that that is ok. While the first option is a good exercise (I did it with Bruch's Kol Nidre when I was 15), the second is more important in the long run.
Like I said, I don't really listen to or watch operas. There are some I like, including newer ones (more specifically Dr. Atomic and Nixon in China, both by John Adams), and if I have the money to see a good opera company perform an opera by a composer than I like, I will do it. It isn't, however, my prefered genre. That said, I don't think that they hold any less intrinsic value than other pieces of music.