I've been playing with Windows 10 on my SP3, and so far it's been a bit mixed. On the one hand, I like where Microsoft is going, in general. In fact, I'd probably stick entirely with the new Start menu and desktop mode, if they'd make the various UI items there just a TINY bit more touchable. On the other hand, it's (as expected) a bit too buggy for me to use full-time, particularly with certain apps that don't work consistently (Corel VideoStudio [crashes on startup], Snagit [crashes on touch], Wunderlist, and some others that escape me).
I'm finding myself logging back onto Win 8.1 when I'm done playing with Win 10 and need to get real work done. Same thing on my desktop (same apps are crashey over there, too), although the Start menu and desktop mode are even more appreciated on that machine. It's SO much more natural and powerful on the desktop--better than Win 8.1 (natch) and a dramatic improvement over Win 7 as well.
Microsoft's doing some great things lately. Did anybody see that Adobe video highlighting the SP3? If anyone can watch that video and not see Microsoft as exciting (again), they're either really stubborn or just not paying attention.