I'm still at the stage of exploring the general landscape of classical music rather than digging around and uncovering hidden gems.
I believe last year I properly began my explorations of vocal music. I got into lieder some time during covid via folk music, seeking out musical settings of poems (mainlynorfolk and liedernet.. great websites!) I believe it was Haydn's settings of Burns (and a brilliant cd by Meredith Hall) that first made me rethink my prejudice against "classical singing" (which I had previously dismissed as "yelling"). I ended up going back and listening to the vocal works of composers I already liked e.g. Schubert. Then Philip Larkin's Selected Letters (great read!) put me onto Handel's oratorios. Then I began investigating the output of various condutors (Hogwood, Gardiner, Pinnock) which led me to Bach's cantatas that I listened to in full (Gardiner & Suzuki) during the first half of this year. I then went crazy over various compilations of operatic arias but couldn't get beyond Mozart, my old prejudice reappeared when I got to Rossini and co. I retreated back to the 18th century and before (esp. Vivaldi, Pergolesi, Purcell). I gave the countertenors a chance (Michael Chance) and discovered countless great albums.
It was only in the last couple of months I gave the post-Mozartian opera fellas another chance. And it was all thanks to this forum! I rarely post, not having much to say, but I spend a decent amount of time reading the Singer Vs Singer threads on the opera board which taught me a vital lesson... I wasn't entirely wrong to feel unsatisfied with the recordings of Rossini etc. I had listened to. Clearly I ought listen to the older singers! I learned my lesson and am now in the process of listening to the older singers (Crespin, Farrell, Caballe, Janowitz, Steber, Sutherland, etc) and their recordings. Apologies to Rossini, Verdi, Puccini and co, the beauty of your music is quite overwhelming.
I'll finish this ramble by mentioning Strauss. The "Four Last Songs" to be specific. Elisabeth Schwarzkopf on vocals.
nonvocal postscript: Argerich's Shostakovich