Academic aptitude is important in a program where most of the classes are only seven weeks long. The aggressive pace means you need to be able to balance a lot of different things at once, integrate new concepts and learn very quickly. GMAT, undergraduate GPA, and a strong transcript are good indicators of academic aptitude.
Leadership potential is important because M.B.A.'s will be expected to be leaders in whatever organizations they join after graduation.
The third component that we look for is really an outgrowth of the fact that the University of Notre Dame has a unique mission. Our founder, Father Edward Sorin, charged the graduates of this University to be what he called "a force for good in the world."
Candidates that can demonstrate a propensity for consideration of other people's needs and the ability to contribute beyond just the "40 hour work week" will generally do well in an environment like the one at Notre Dame, and so they will typically make a favorable impression on the Admissions Committee as well.