Brian Ferneyhough is a scary composer for many people. Or at least his music is deemed to be scary. By 'scary' I mean highly complex. And yet I find much of his music very direct and even Beethovenian in manner. It's Beethovenian in that it often has a strong sense of forward direction; which much post-serial and experimental music doesn't have. (This is despite the fact that I'm sure I can recall Ferneyhough speaking out against what I think he called the “fixation with linearity” in Western music.)
This is a classic case of the disjunction between music being complex in terms of its form and composition and it being direct when it comes to actually listening to the music. After all, many baroque fugues and Renaissance polyphonic masses are very complex; though often easy to listen to (though not too easy, of course).
It must be said that when you hear Ferneyhough speak, he does strike you of being a bit pretentious. Though perhaps that's simply because I'm stupid or very cynical.
Ferneyhough as Instrumentalist
Ferneyhough is a great instrumentalist. That is, he is a great writer for all manner of instruments – from the low brass to the piccolo. This isn't always the case with accomplished composers. I would say that Alfred Schnittke, Webern, Ligeti, etc. are great writers for various instruments; though many post-1945 composers haven't been. Indeed even some classical masters weren't really that accomplished when writing for certain instruments. I personally think this is true of Beethoven, save for the piano and perhaps strings. I also find Brahms symphonies badly scored in that they sound much too dense. (Incidentally, I find this true of Beethoven too.)
Many of Ferneyhough's works features solo instrumental writing even within ensemble pieces. Thus in one of his string quartets it begins with one violin, then two, etc. In one part of the Carceri d'invenzione we have a marvellous trombone and piccolo due which opens that work. This pairing down of ensemble pieces (as well as pieces for string quartet and orchestra) frequently occurs in Ferneyhough's oeuvre. In that sense, it's a little like Bach's Brandenburg Concertos.
Ferneyhough has also written many pieces for solo instruments. These include pieces for piano, violin, flute, piccolo, bass clarinet, guitar and so on. These are surely in the tradition of Berio's Sequenza.