Chapter three of Ursula K. Le Guin’s Steering the Craft is devoted to sentence length and complex syntax. She says, wisely:

Rhythm is what keeps the song going, the horse galloping, the story moving. Sentence length has a lot to do with the rhythm of prose. So an important aspect of the narrative sentence is–prosaically–its length.

And then there is this bit which is pure gold:

When Henry James began dictating his novels to a secretary, his tendency to qualify and parenthesize and embed clause within clause got out of hand, clogging the narrative flow and making his prose totter on the edge of self-parody. Listening with a careful ear to one’s prose isn’t the same thing as falling in love with the sound of one’s voice.