The system font has been changed to a much more pleasing font, and it is displayed at 14 point, not 12 point. Application-specific options are held in the new Application Menu, which has replaced the Apple Menu. This takes a LOT of getting used to, and even after you do, you are left wondering whether this is truly the best way to go about laying out a menu structure. But it is handy when users are only looking for something that is application-specific. However, it is likely that Apple may offer a backwards compatibility option in personal settings.
All disabled elements are grey, while all active elements are a very lush blue.
One of the drawbacks to Aqua is that the buttons are much larger than their Platinum counterparts, so any applications that hasn't been Aquafied will need some work. Otherwise, buttons that look just fine in Platinum look will overlap very unattractively in Aqua. There are some other problems which show the relative immaturity of the new Windowing system in Mac OS X. Windows, which now resize and update their window content on the fly, resize very unresponsively and slow the system considerably. And Windows that go from being the active window to a background window and then back to an active window can end up retaining the transparent window of a background window. Pull-down menus with many elements end up displaying invisibly, until a user runs their mouse over where the menu elements should be.