I nominate

Alfred Schnittke- Viola Concerto.  A late twentieth century Harold in
Italy- but now the viola witnesses and comments on not Italy, but the
worst of the twentieth century.  Powerful and eloquent and beautiful in
its way.

Close contenders:

   Ingram Marshall: Gradual Requiem
   George Tsontakis: Four Quartets for Orchestra
   John Adams: Naive and Sentimental Music
   Per Norgard: Third Symphony
   Alfred Schnittke: Eighth Symphony
   Alfred Schnittke: Concerto for Piano and Strings
   Andrew Violette: Piano Sonata number Seven
   Anders Hillborg: Clarinet Concerto

Bernard Chasan