Looks like it's going to be a long summer for the Windows PR team; also see Windows 10 Launches Today. But We're Still Waiting For the Important Stuff (Wired)
"But the question is not whether Windows 10 is a good upgrade for Windows 8 users -- obviously, it is. The real question is whether Windows 10 deserves to supplant Windows 7. Despite substantial new functionality in Windows 10, Windows 7 users should wait until the upgrade train brings more improvements.Windows 10 review: Hold off if you use Windows 7 | InfoWorld
Many of the new features of Windows 10 do not seem ready for prime time, including the greatly modified Start menu with live tiles, the new Edge browser, Cortana, and the Continuum method of switching between mouse and touchscreen control. They all work well enough, yet they all lack key capabilities. The lesser tile-based Windows apps vary in quality from good (Mail, Calendar) to passable (Photos, Phone Companion) to barely breathing placeholders (People, Groove Music, Movies & TV)."