Well, when you see Vista alone, it is a decent OS with vast improvements over its predecessors.
But, when i see this video over there at google video about OS X and than compare it to my experience with Vista, Vista lacks a lot of things.
In OS X, everything runs smooth, there are animations that look cool but don't prevent you from doing useful things. In Vista, you can count animations and transitions with the fingers of one hand. That's so boring!
Vista did include rudiments of stylish animations and such things back in early longhorn 4xxx series alpha builds before they decided to go on with win server 2003 sp1 bits. In the 4xxx series builds Avalon was the key technology for presenting the whole UI of Longhorn, but Avalon still was in development and it's not a good idea to build the UI of a OS on a technology that itself is still in development. This and other things were the reason for Microsoft to make a restart in the development of the OS we now know as Vista.
Now, the whole UI in Vista is based on Win32/GDI technologies, mixed with stuff that's new in the 2007 Office System (Net UI). The only thing that's based on Avalon or Windows Presentation Foundation, as it is called now, is the Desktop Window Manager (DWM) which is responsible for the only few animations we see in Vista, namely the minimize and maximize animations, flip 3d and such things.
Windows Presentation Foundation is still in Vista but only used for the DWM, as stated before, and as a plattform for software that still has to come on market when Vista is done, but no WPF in Vista's applications itself, so no cool transitions in the application windows itself, so no OS X like style.
I hope that MSFT is able to deliver a comparable UI experience in terms of animations and transitions in Vista R2 or at least in Codename "Vienna", Vista itself won't be on par with OS X in these departments. That's a pity!