David Pierce, writing for The Verge:
Familiar is easy, it's safe, it's probably profitable. But in an industry that moves as fast as technology, familiar is dangerous.
Beside the name "Windows 10" which is a bit odd, I believe this is the right move for Microsoft and for Windows: an OS that is not too fancy and pretty conservative (in a good way). Pierce is right to point out that it can be "dangerous" but the innovative and "risky" Windows 8 did not really pay off.
It's telling that throughout its entire event, Microsoft seemed to be speaking not to Windows 8 users, but to the customers who took one look at live tiles and decided to stick with Windows 7 or Windows XP.
My bet is that the vast majority of Windows 8 users are using it as they would use Windows 7 anyway: a desktop-centric OS. Microsoft is smart for improving this experience for 95% at least of its customers. If the touch-hybrid-Windows 8-PC vision has to die with it, they seem to be willing to do that sacrifice, leaving touch-first UI for the mobile devices only (à la Apple iOS / OS X).
UPDATE: Nick Statt at CNET has a good theory on why Microsoft decided to name it Windows 10 instead of the expected Windows 9.
FOLLOW UP: Tim Moynihan over at Wired shares the idea that Windows 10 is a smart move for Microsoft:
Not many people wanted the hybrid desktop/touch OS of Windows 8. Likewise, they won’t want hybrid adaptive software that offers a crappy experience compared to true mobile apps. But Microsoft had to do something to boost its presence in the mobile OS market. It’s no sure thing, but Windows 10 may be the only way to do it.