A simple way of describing his music is... *"musique concrète instrumentale". The notion is the creation of a subtlety of transformation of timbre, a manipulation of a continuum from sound to noise, from pitched notes to pitchless textural exploration, and all that in the sphere of (mostly) purely instrumental music. That means that in Lachenmann's music, there's a world of sound that rivals and even surpasses what electronic and electro-acoustic composers can achieve. -Guardian.
Essentially, he is a acoustic composer writing electronic sounding music. He is somewhere in-between the timbralist composers like Iannis Xenakis/James Dillon and the spectralist like Gerard Grisey/Trsitan Murail. But his compositional 'reason d'etre' is often hidden. He is an individual, creating new sounds that amaze audiences. Also, his scores are untouched by the 'new complexity' which means that his scores can be relatively simple.
*The phrase, "musique concrète", comes from Pierre Schaeffer, one of the pioneers of electro-acoustic music in the 1940s.