Well I installed this on my work PC, it's pretty cool. I ran earlier builds of the tech preview so knew what to expect. I'm disappointed they went the way of white on white UI, I am still utterly baffled and wonder if any of these companies, apple/google/Microsoft, use their devices in the dark.
Overall I don't see much of a change versus win8 on the desktop side. The start bar is semi useless, don't really care about apps and I would rather see a list of ALL my programs with menus and submenus, easy fix just installed classic start menu. Cortana seems cool, but you have to give up a ton of privacy. Not more than Google I'd suppose, so I'll probably use it. The Edge browser is completely useless, the Metro 8.1 browser was MUCH better. Although I use desktop IE11 on my desktop anyway so I switched back to that. Edge browser seems like something they would have done on win8, cram tablet use to desktop users, very odd they made it the default browser IMO.
What I'm mainly hoping for is speed improvements and efficiency, I'd be happy with that and no new features. For desktop use it seems decent, although I won't update my home system as I can't lose OneDrive placeholders, at work I use OneDrive for business which never had placeholders anyway. I won't install on my tablet either as win8.1 is much more tablet friendly.