From Joan Acocella's review in The New Yorker:
Why is he so popular? One reason, I think, is that he gives people the modern pleasure of seeing abstract work without leaving them scratching their heads over what it was about. Though he may not have a story on the surface, he always has one underneath, in the form of movement motifs. For every dance, he devises a certain number of key gestures, which he then weaves through the choreography. Some of these gestures are naturalistic. In “Mozart Dances,” for example, there is one that could be called the “danger” motif: the dancer suddenly turns and looks behind him, as if he had heard a strange sound, and then looks back at us as if to say, “Did you hear that?” But others of Morris’s motifs have no obvious meaning when he first shows them to us. Only in the course of the dance do they come to tell a story.