Too many to list.
To sum up it is more stable and already better supported than Vista was at launch.
DirectX 11 is a much better step above the previous DX iteration than DX 10 was.
Security is much better.
More customizable and feature rich.
User interface very pleasing.
Faster than Vista/XP.
Optimized for multi-core CPU's.
A quick trip through Google will give you more.