I was ready for an all-new look in Leopard; I was ready for Aqua’s successor. That Leopard doesn’t provide that is a disappointment, but hardly a sin. But a lower degree of difficulty should entail less risk. Viewed in that light, Leopard’s graphical missteps are damning. If Apple is going to make mistakes, let them be made in service of a truly daring design. I’m willing to forgive, and even to look back fondly on the original Aqua UI for this reason. But to attempt a relatively tame evolution and then to willfully screw things up—things that were not broken before—that I do not forgive.
Mac OS X 10.5 Leopard: the Ars Technica review