I tried Windows 7 Ultimate pre-Beta version. Its still under testing. And it of course have some flaws which are getting better with every update.
I must say that this is not that bad. Windows after releasing Windows Vista might have realised that it was an extreme releasing making it unable to work on most of the PCs. Vista's requirements were quite high and non-economical. But people who were able to run on their machines said, its cool! And it was. Graphics, Speed, features were terribly good! Features like Ready boost were added.
To counter act the incompatibility of Vista, Microsoft came with Windows 7. Windows 7 is compatible even with some 5 year old computer. It runs with no graphics card. :) Requirements are optimal.
Looks of Vista with features of XP - This is how I can best describe this OS.
The traditional taskbar is given modification. No differentiation between the quick icons and the regular minimised windows. All look same. This new one actually sucks! Thank god we can change it to the traditional taskbar.
The glossy look of Windows Vista are restored.
Paint and calculators are given some modification too. (I thought Microsoft had forgotten those applications)
Best thing that I happened to see is the Action center. If something goes wrong, the OS can self diagnose the machine for troubleshooting. Its really cool!
The animations are simple and don't eat away your RAM as much as Vista did.
I heard that the Microsoft is going to give some good Bluetooth Support in its Beta version.
I still use my Windows XP as second OS.