One of the main (only?) improvements in Vista for gamers would be the inclusion of DirectX 10. And to make gamers upgrade, they made DirectX 10 a Vista exclusive. Is it worth it? See for yourself.
Above are two screenshots of the same game rendered in DX9 and DX10. Can you tell which is which? Maybe you need to see the larger versions after the jump. Can you tell now? If not, then it's probably not worth it.