Good ballet is constructed with a sense of discipline, form, line, and pattern, and with conscientious attention to the music. It is engaging to the eyes, the mind, the emotions, and the body. Part of the great allure of any dance form resides in the visceral thrill of the movement itself - feeling in your own body some physical reaction to the movement onstage.
In the traditional ballets, form is created by a story line, which can range from heartbreaking to ludicrous, and often includes a great deal of mimed action to convey meaning. But the story is usually transcended by the beauty of the movement itself. Even if we can't totally buy four young women as cygnets, we can appreciate the gentle swanlike shifts of the head, the precise, intricate footwork.
Generally, story ballets are structured with a blend of pageantry, dances that convey the action of the story (especially crucial pas de deux between the main characters) and divertissements (large ensemble dances or smaller virtuosic pieces that are merely diversionary showcases). Ballet companies these days often restage these classics, shortening and updating the choreography to appeal to more contemporary tastes. And sometimes even the most revered classics are completely redone by living choreographers - thus the many versions of works such as "The Nutcracker."
In contemporary story ballets, mime is generally replaced by more integrated gestural movement that doesn't stop the flow of actual dancing.
And in abstract ballets, it's the movement itself that offers reward. With his "Les Sylphides," Michel Fokine turned ballet on its ear by dispensing with a story line and creating instead a "ballet of mood."
With his glowing "Serenade," George Balanchine helped establish the pure-movement ballet in the United States, following with a stunning repertory of ballets inspired more by a specific piece of music than any kind of narrative.