I spent all day writing program notes for the Shostakovich Eleventh Symphony, and I finally pinpointed why I can’t love his music as much as I do Mahler’s. It often demonstrates the same contrapuntal saturation, timbral variety, and rhythmic drive as Mahler, but it lacks meaningful background harmonic movement. A foregrounded chord, tensely sustained, will finally shift to another chord – and then back again, instead of onward toward another, continuing harmony that would make the move seem significant. Long sequences are not unified, as they are in Mahler, by a large-scale voice-leading that leads somewhere. Instead, the large-scale harmony wavers, and fluctuates, and diddles around, leaving the impression that he’s just stretching out the length without a goal in mind. The melodic aspects are great, but the tonal background has no tautness. You can feel the approach to an inevitable Mahler climax ten minutes in advance, but Shostakovich, for all his many virtues, just too often feels harmonically arbitrary. And, as a composer, large-scale voice-leading is one of the things I pay most attention to in my own music. I’m kind of fanatical about it.
And whatever legitimate oppressive hardships Shostakovich had to work under, I doubt that Zhdanov and the Communist Party Central Committee ever cracked down on large-scale voice-leading.
[AFTERTHOUGHT: By the way, I don't say here that Shostakovich wasn't a great composer. I say that I can't love him as much as I do Mahler (one of my very favorite composers) because I'm highly attuned to large-scale harmonic movement. On a good day I'm very precise in my formulations.]