Too many of my friends have found the Win10 upgrade to be a total nightmare, with "Something happened" errors, slow running, and malfunctioning programs. I'll use it (or possibly its successor) when I finally have to replace my current computer, and not a moment earlier!
In fact, I've met precisely one person whose upgrade was initially said to go through without problems. However she has now found that her computer's performance has dropped, and improving it has required the wholesale re-installation of programs. And she's still not completely happy with the way it's running.