Aside from pretties, most of the control items have been overhauled to work smooth like buttah. The left pane introduced in XP is now useful, the address bar in Explorer is replaced with breadcrumbs, tons of visual and interface features that make use of your 3D horsepower that's been wasted up till now (like Apple did with Quartz Extreme) such as real-time window previews and thumbnails, transparency, etc. Nice little details like the new search interface and more functions incorporated into the taskbar. The Start Menu is like 100 times better than either the new one in XP or the classic model. And gadgets which are useful little mini-apps always at your fingertips, like the Widgets in OSX.
ordinary desktop shot
new Start Menu "All Programs" section
pointless but nifty visual effects (Win+tab task switching; Alt+tab functions as normal but shows previews too)
Wiki is an easy place to find more screenshots and description of the small details:
http://en.wikipedia.org/wiki/Windows_Vista
http://en.wikipedia.org/wiki/Windows_Aero
For the most part it isn't mind-blowing. It's just... good. But really good.