Metallic paint is made of tiny flakes of real metal floating in a clear binder. It's the light reflecting from all those bits of metal that create the "metal finish." But though the microscopic flakes are real metal, they don't line up evenly, so they bounce light around rather than reflecting it directly back at us like a mirror. This is why metallic painted surfaces always have that soft, flat look. The finer the metal flakes and the clearer the binder, the more reflective the surface will be.
Click for larger view