Windows Vista is designed to be a lean, mean, secure machine. Security is a top priority at Microsoft with many low-level systems rewritten to avoid future "Blaster" type worms. It’s getting an all new presentation system called Avalon along with a whole toolset of new ways of creating really cool and useful software (XAML, integrated .NET, Indigo, etc.).
And while the jury is out on how polished the final product is going to be, Microsoft is taking quite seriously the need to deliver a secure, solid, and visually appealing OS into people’s hands next year. When beta 1 ships, we’ll do a second round preview that we can go into more detail with.