We're playing this piece in band right now, and its really great, there are so many things to say about it. First of all the fact that it revolves around the theme built upon only four notes, b, a, c and b-flat. Tonally, its such a unique sounding piece most of the time. The opening has a muddy texture in which the main motive is displayed randomly and jumping out of the texture. The "accompaniment" meanwhile, is built upon an octatonic scale giving a winding, and mysterious quality to the piece.
The theme is presented over 24 times throughout the course of the piece which is really one of the most interesting things about it. Its difficult to really pinpoint the structure of this particular passacaglia simply because the melody is repeated so frequently. Its almost difficult at times to pinpoint who has the melody because it creeps in and out of the texture almost seamlessly, and in so many variations that you really have to listen at times to even realize that you could have the main motive, or some form of it.
I really like the tension and the transformation that the piece undergoes, the tension is constantly being built through rhythm and tonality and then released which is satisfying to me.