UPDATE: What I intended to mention here, is that there is absolutely no mention of Shostakovich in the counterpoint text, which peters out rather unconvincingly with a little Hindemith, a piece from Mikrokosmos by Bartok and the Great Chorale by Stravinsky--surely, all of them rather trivial examples of counterpoint when set beside Shostakovich?
So due to this litany, theorists and historians have tended to have a blind spot and smack in the center of it is Shostakovich. He was parodied by Bartok and ridiculed by most composers in the main stream of 20th century practice. Why? He didn't follow the correct technical progression and was therefore seen as an apostate (or hack). This was often attributed to the political repression in the Soviet Union that forced him to write music conforming to 'socialist realism' with its insistence on the use of folk song, the avoidance of 'formalism' (a word for the influence of Western avant-garde music) and the creation of an heroic effect.
Now an argument could be made that some of Shostakovich's music, the more public genres such as symphony, for example, do show a superficial conformity with the demands of socialist realism. Discussion has raged around this question and I don't want to take it up here. A good locus classicus for it is the article by Richard Taruskin "Public lies and unspeakable truth: interpreting Shostakovich's Fifth Symphony" in Shostakovich Studies, edited by David Fanning.
The Twenty-Four Preludes and Fugues for piano, op 87, composed in 1950-51, did raise some opposition as they seemed to many to be a bit outside the path that Shostakovich was supposed to be following and it took a masterful performance by the dedicatee, Tatyana Nikolayeva, for the Committee for Artistic Affairs to give authorization for publication.
These pieces, the first successful attempt since Bach to write preludes and fugues in all the keys, were the fruits of a Bach competition that Shostakovich was present for in Leipzig, celebrating the 200th anniversary of Bach's death. Prior to this he had not been particularly disposed to the fugue genre, but he ended up writing a prelude or a fugue every few days for the next couple of months.
The result was a work of real racination, in my neologism. I talk about that here. Sometimes in music history, composers find themselves in a situation where the only solution seems to be to go back to some fundamental spring of music, some bedrock, and start all over. This happened around 1600 and again around 1970. I think that Shostakovich is doing something similar here--rediscovering fundamental things about counterpoint and harmony. Let's look at the first fugue in C major. It is so totally in C major that there is not a single accidental in the entire 106 measures. Here is Nikolayeva playing the Prelude and Fugue in C major. The Fugue starts around 2:31:
This sounds nothing like a Bach fugue, of course. For one thing, it is as much modal as tonal. When Shostakovich has an entry on E, he makes no attempt to inflect to E minor. Similarly, when he makes an entry of the subject on B, it results in the Lydian mode with the perfect fifth of the subject becoming a diminished fifth [UPDATE: Lydian mode would give you an augmented 4th. This is actually in Locrian mode, but who has ever heard of Locrian mode?]. Despite the adherence to fugue style, it comes out as Shostakovich. A piece of music like this is a repudiation of the unspoken assumptions of the 20th century avant-garde which we might summarize as the following: thou shalt not write tonal music, or if you do, it has to be a 'wrong-note' parody like Stravinsky's Great Chorale from L'Histoire du soldat; thou shalt not attempt to revive outmoded musical forms, again, except as parody; thou shalt develop thine own unique style with as little reference to other kinds of music as possible and finally, thou shalt move through different periods in thy work so as to seem fashionable.
Op 87 by Shostakovich is about as far from these strictures as possible. Perhaps this is why the work was not taken seriously for a long time. It does take some listening. At first I heard little of interest there. But, like the Bach Art of Fugue it grows and grows on you. The preludes are a diverse collection of musical styles. The one in B minor is like a Baroque overture:
But the fugue that follows is odd. The subject is stated in octaves, but then another subject, or countersubject, is stated separately. Then they join together. That second subject provides much of the development with the first coming in occasionally, sometimes in stretto. The harmonic layout also is like nothing Bach would have done with entries in G minor and C minor. The one thing that seems clear is that this is a serious piece of music, a profound meditation...
I haven't put up an analysis of these pieces as I often do with Bach. In fact, outside of a few Russian theorists, I doubt anyone has analyzed this music! But more and more people are beginning to appreciate op 87 and I have even seen one claim that this is the greatest piano work of the 20th century. You know, that wouldn't surprise me a bit.