3. Windows Start Menu meets Metro.
I hated when Microsoft opted for Metro both in Windows Phone and Windows 8. This is one of the major reasons I skipped 8. I know 8.1 has ironed out some of the problems but 10 brings familiarity back to the workspace.
Left side is the Start Menu while right is Metro. If you want a full metro screen just click the top right maximize icon. Microsoft allows you to decide what you want so neither party seems left out. A huge improvement.