It's not just different. It's bad design. Removing the start menu and replacing it with a touch interface is just plain stupid.
The metro start screen doesn't replace the start menu, all of the functionality that is currently part of the start menu is seperated out & you can use Windows 8 without ever using the start screen.
I don't think the start menu is that important, I spend very little time using it each day. So getting used to Windows 8 isn't going to be a huge leap for me. I lent my Windows 8 netbook to a teenage relative when they visited for the weekend and they never said a word.
I love some of the other ui improvements.