There must be an objective measure of its success. In particular, it must be experimentally verifiable. Einstein's theory of relativity involved creativity and insight, and at least in my mind, is a beautiful construction of the human intellect. However, had it not given the correct prediction for the perihelion shift of Mercury, or for the bending of light around the sun, it would have been irrelevant, and failed as a scientific theory. Experimental results must be interpreted using concepts which, as stated above, are themselves subject to change.
Modern physics is currently at an interesting crossroad.
String theory, which may one day replace relativity and provide a unified theory of everything, is beautiful, complex and involves a great deal of creative genius on the part of its proponents. It has not yet met the true test of science, namely to make a falsifiable prediction. It is therefore pushing the boundaries, not just of human knowledge, but also between science and art. In these notes we will try to instill not just an understanding of physical concepts as they are currently accepted, but also an appreciation for their beauty and the intellectual leaps made in their discovery.