Vista -> Win 7 - huge architectural changes, lots of improvement to file system, kernel, lower layers, changes to Explorer, desktop.
,br> Win 7 -> Win 8 - again major changes (even if you ignore Metro), new task manager, kernel hibernation, File history, MS account
,br> But so far, everything about Windows 10 is focused on Continuum, mobile etc. The only new thing on the desktop is the revamped start menu and virtual desktops, Cortana. It's the same desktop, same Explorer, same internals, just a few color and icon tweaks. There has been no information about what's actually new underneath or how its better. It's now been 2 public announcements and they haven't talked about a single engineering feature except DX12.