What makes a ballet or music performance excellent?

I know the basics, the bare minimum for something to be a good performance--the ballet dancer can perform all of the technical aspects of the choreography skillfully while maintaining a calm, graceful countenance. And a skilled piano player knows how to play the right keys that match up with the notes on the page.

But what makes for a great performance? If the choreography is the same, wouldn't dancers simply be technicians executing a preplanned set of movements? Why do people rave about hearing Yo Yo Ma play over other cellists playing the same music?

Please, before angry ballerinas/ballerinos/pianists/cellist/xylophonists come in to castigate my philistine understanding of the arts, I'm always impressed by dancers' and musicians' skills! I just don't know what separates a good, capable dancer/musician from a Nijinsky or Copeland or Bocelli.