My last year of college I discovered Henze by accident.  I was diggin
through music to play for my senior recital when i found a Marimba solo
written by him(Scenes from a Snow Country).  It was very, very twentieth
century - it used the tone row, lacked bars lines, and was incredibly
impressionistic in it's style.  Well, since then I have bought some stuff
by him - my favorite has been his Requiem.  As you mentioned, it really
hasn't stuck with me so much - but all the same I like listening to it
for the experimentation of tone color - the different techniques - and
you know, some of it just sounds neat.

Jeremy