It's hard to recommend pieces by Krenek without knowing the preferences of the person I am speaking to. Krenek is often maligned for having been so incredibly prolific and working in every fashionable style during his long life (1900-1991). He simply wanted to stay on the cutting edge, so one can only admire his willingness to try new things.
As for the prolifix, I am reminded of a perhaps spurious anecdote: a cellist was performing a three-movement solo cello work of Kreneks, and the composer was in attendance. The performer had decided to swap the 2nd and 3rd movements for the performance. Afterwards, Krenek asked him about this, and the performer replied, "It made more sense that way, and considering that I spent more time practicing the piece than you did composing it, I feel justified in making those kinds of decisions." Krenek took it pretty well, I understand... but of course I'm paraphrasing, and it does sound a lot like Urban Legend. (no, not michael tilson thomas' parvum opus for contrabassoon and orch)
I am afraid I don't know his op. 180, but here is a sample of pieces from various periods that I recommend (in no particular order and with no particular agenda):
Reisebuch aus den österreichischen Alpen (text by the composer), op. 62
Inspired by and explicitly dedicated to Schubert (actually quite catchy)
Lamentatio Jeremiae prophetae, op. 93 (1941–2)
a cappella setting of the entire Lamentations text in the twelve-tone technique -- quite possibly the most remarkable a cappella choral work of the 20th century (I guess that isn't saying much).
Sestina for voice and ensemble, op. 181
a remarkable work in the serial idiom, where durations, pitches, and text are organized according to the same structural principles. Very hard to find a recording, unfortunately.
For a discussion of the structure of a sestina (a medieval poetic form) see
http://en.wikipedia.org/wiki/SestinaIt's essentially 12th-century serialism! Take that, modernism haters!
Parvula Corona Musicalis for string trio, op. 122
after JS Bach (recorded by the trio recherche on hatArt label, I think)
Karl V (opera on an original libretto) op. 73 which is pretty heavy, but I prefer it to
Jonny spielt auf.
Of course he is most famous for
Jonny spielt auf, but that piece has a lot more to do with the politics of including jazz than with jazz music itself.
Of his string quartets, I most warmly recommend the 5th and the 7th. The complete quartets were recorded by some people once... the Sonare Quartet on the MD&G label.
Krenek is better known in the United States than in Europe, since he lived here most of his life, and died in Palm Springs. We (Sydney Grew and I) intended to start a thread on Krenek, but now you have done it for us, thanks, pim_ !