Leopard is, at once, a major alteration to the Mac interface, a sweeping update to numerous included productivity programs, a serious attempt to improve Mac OS security, and a vast collection of tweaks and fixes scattered throughout every nook and cranny of the operating system.

As with every OS X update since version 10.1, there’s no single feature in Leopard that will force Mac users to upgrade immediately. Instead, it’s the sheer deluge of new features that’s likely to persuade most active Mac users to upgrade, especially since this is the longest gap between OS X upgrades — two and a half years — since the product was introduced. Sure, some items on Apple’s list of 300 features might seem inconsequential, but if even a handful of them hit you where you live, that will be more than enough motivation for you to upgrade.

A new look
Apple trumpets the interface changes in Leopard as “stunning” and “eye-opening,” but in reality the changes are a mixed bag.

First, the good stuff: After years of experimenting with different looks for windows, sidebars, and other interface elements, Apple seems to have settled on a fairly consistent interface. The color scheme is largely monochromatic—shades of gray with slight gradients. Apple has improved the contrast between the frontmost window and the rest of them by increasing the top window’s drop shadow and dramatically lightening the color of inactive windows. The Leopard Finder’s new sidebar, clearly modeled after the iTunes Source List, is better organized and more usable than its Tiger counterpart.