Windows 95 - nothing to really compare with
Windows 98 - more windowsish
Windows 2000 - haven't tried, but was very popular
Windows XP - they haven't thought that people like MS so much, they have added a whole new kind of interface
Windows Vista- they thought that they can do anything right - they were wrong, but they've created aero
Windows 7 - MS kicks ass after the failure of vista with the best performing os ever, improoved aero look
Windows 8 - ?