I am using Windows 10 "Technical Preview" on my personal laptop, although not on my work laptop, which still has Win7. I really can't stand Win8 and that's why I'm not using it, even though I was offered it.
My opinion is that Win10 is most definitely not ready for release yet. Different people with different hardware will experience different problems, but in my case, it's a matter of apparently random chance how the screen will look when I boot it up. Some of the time, all the fonts look just fine, but at other times, smaller fonts and some of the small icons look blurred and malformed.
There are occasional application crashes, particularly with Photo Viewer.
It seems unable to join a Homegroup made up of Win7 computers.
However my biggest gripe with Win10 is this: what exactly is the point? If you're using it, as I do, in the kind of "classic desktop" mode, it looks very much like an uglier version of Win7. Everything has the Win8 "flat" appearance, with unattractive desktop icons and application windows.
On the other hand, there are a couple of things I do like, such as the integration with OneDrive, which means I can access important files at home, or anywhere with Internet, and on my mobile phone.
No doubt I have some more work to do in order to discover the other good stuff within Win10 as well.