A fifteen-year-long wait for the "Aha!" moment...

This is how long it seems to have taken Paul Griffiths - a very experienced music critic and a perceptive writer on modernist music in the 20th century - to change his mind about one of Helmut Lachenmann's most often performed orchestral works: 

Mouvement (vor der Erstarrung) for eighteen-piece ensemble is quite successful in the avoidance [of anything pleasant to listen to].  [It is] a landscape of rustlings, scrapes, electric bells and pointless percussion toccatas. (The Times, July 8, 1986)

[In] Mouvement (vor der Erstarrung) ... there are a lot of whirrings, scrapings, knocks and breathings. But not only are these noises beautifully made in themselves, they also add up to a bracing musical design. ... This omnipresence of sheer sound contributes to the poetry of Mouvement...  It comes as if from nowhere, takes you firmly by the hand and will not let go until it has shown you things you could not have suspected.  (New York Times, November 4, 2001)

For lack of better things to do, I briefly wondered about Griffiths' long delayed epiphany.[1]  After all, Lachenmann's Mouvement is neither intimidatingly complex (compared to, say, Carter's Double Concerto or Concerto for Orchestra) nor aggressively abrasive (unlike, e.g., the music of Xenakis or even Beethoven's Grosse Fuge).  For the most part Lachenmann's piece speaks quietly and delicately, and its large-scale structure is essentially that of three superimposed arcs representing gradual changes in pitch content, dynamic levels, and the density of texture.  In the manner of Hollywood screenwriters pitching an idea for a movie, one could simplistically describe Mouvement as Ravel's Bolero re-composed by Webern and performed on ingeniously adapted objects from the inventory of a hardware store.

In the end, I decided that the Griffiths case is an example of Charles Rosen's observation that the initially off-putting and disorienting effect of new music has to do not so much with what the composer put in the score as with what he left out, be it resolution of dissonance, themes, repetition, unified tempo, or identifiable pulse.  In Lachenmann's music, what is left out - the primacy of pitched sound over unpitched noise as the raw material of composition - has been accepted as fundamental even by avant-garde composers from Varese and Webern to Boulez and Stockhausen.  It is then not surprising that, on first encounter, Lachenmann's sound-world may strike even experienced listeners as being so alien that it will defy all prior expectations of what avant-garde music may sound like.

But enough of this amateurish musicology.  Whether or not one eventually comes to terms with Lachenmann's music, his Mouvement certainly offers a deeply unsettling, utterly fascinating, and absolutely unforgettable journey into a realm of previously unimaginable musical possibilities.  I cannot think of a better guide for this journey than a concert performance by the Ensemble Musikfabrik under Peter Rundel recorded in 2015 at the Concertgebouw, Amsterdam.  As an alternative, there is a slightly cooler performance from a 2015 concert given in Essen by the ASKO|Schonberg Ensemble under Reinbert de Leeuw.  Finally, for those not familiar with Lachenmann's music, it may be fun to watch a concert performance of Mouvement by the Ensemble InterContemporain (which commissioned it) in this superbly produced HD video (choose 720p, not 1080p, quality for best sound).
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1.  These two are the only articles on Lachenmann's Mouvement reprinted in Griffiths' collection of his writings as a music critic.  Incidentally, his short 1994 book on 20th century music does not even mention Lachenmann, although it gives space to the music of Philip Glass.  By 2010, however, Griffiths had accepted Lachenmann as one of the most important and influential composers of the 20th century.