Berg - Wozzeck.
Why have I spent my life not listening to this? I don't really know, except that I guess I got it into my head when young and impulsive that being mad about Bartók disqualified me from liking the Second Viennese School. Well, I don't like serialism, but this is not serial; and it's so lush and romantic and human, and the orchestral writing looks forward to Hartmann (and back to earlier Bartók in places), and the operatic writing points ahead to Britten (Peter Grimes and Curlew River in particular) - what's not to love and admire?
Look to find it in the mediaf!re thread shortly.