Wow, Rihm at his most expressionist... Isn't it amazing to see (hear) how Rihm's compositional voice had already fully matured by his early twenties (this symphony dates from 1975 when he was just 23).
It is an opinion to state that you don't enjoy this music. It IS painfully ignorant, however, to state there there's no talent behind this music or that anyone can do it. Schoenberg's music is highly personal, well crafted and intensely expressive. Also, listen to his early, still tonal works like Verklärte Nacht or Gurrelieder and you'll see that even in the tonal vein Schoenberg was a highly accomplished composer.
I agree that Rihm's first String Quartet is not yet on the same level as his later, mature string quartets. Still, it's amazing to realize that Rihm was only an 18-year-old boy when he wrote this music.
Something's telling me that this sketchbook is a fake...