No revolution compared to Vista and XP: the interface is improved (notammen window management) and reactive; the handling requires no effort of adaptation.
The compatibility with older programs designed for Windows XP and Vista has improved significantly. It is also very nice to be able to benefit from the Media Center (DVD playback) and backup. This avoids to buy expensive third-party software and often less reliable.
Finally, the system looks very stable.
In summary: Windows 7 preserves your investment (learning and applications), while increasing reliability. It is for me what I ask first.