Nothing really major - most people say it's basically the same as vista, but they've worked on it getting started faster and also taking less resources.
There's also some kinda GUI changes, but whatever... it's windows.
The only feature that I found really big potential for is the "snap to 50%" of the screen when you drag a window to the left or right of the screen. It should be a nice (and long overdue) change from having to open windows and right click on the taskbar and "tile windows vertically" all the time.
As far as gaming goes, there's DX11 which seems to be a superset of DX10, with probably the most "impressive" feature seemingly being tesselation... which most likely isn't going to give the end-user any benefit.
Altogether, it might actually finally push me over XP. I've been more than happy to ignore vista since it came out.