Paul Thurrott took a look at the first release candidate of Windows Vista:
Microsoft has made dramatic changes to Windows Vista since the May 2006 release of Beta 2. Many of these changes come under the hood. For example, RC1 is noticeably more stable and offers dramatically better performance than does Beta 2. Games, suddenly, work just fine. Microsoft tells me that it expects Windows Vista to run most video games as fast as does XP, and that's one performance metric I'll be measuring in the near future. Certainly, modern games like "Half-Life 2" suddenly work fine in Vista. These games were utterly unplayable in Beta 2.