I think that we are seeing the usual problems that attend any O/S release, except that they are being compounded by problems with Windows Update. Microsoft has issued some bad patches to Windows Update that, in some circumstances, make it hog system resources and run very, very slowly (if at all). These problems are present on Windows 7 and all subsequent releases, and can manifest themselves during attempted upgrades to Windows 10 since this process also uses the Windows Update service. Routine updates to Windows 7 through 8.1 are also affected.
Microsoft seems to have been very coy about this problem and no explanation or definitive solution has been offered. Various "fixes" are available but they all involve using Windows Update, the very software that is broken. There is, of course, the Windows Update Stand-Alone tool (WUSA). The only problem with this is that it insists on the Windows Update service being started and it is this that slows everything to a crawl. It ought to run in safe mode but it won't since the Windows Update service can't be started in safe mode. What a dog's breakfast!
My laptop (running Windows 7 32-bit) is busy updating itself. It has taken all night to decide that 37 important updates need to be applied. It claims to have downloaded 76% of 155 MB but is timing out since the update service is making it run much more slowly than usual. Since typing the last sentence it has jumped to 96%, so maybe it will start applying them soon. I shall leave it running for as long as it takes. Hopefully, normal (Windows Update) service will then be resumed.
As for Windows 10, it would be silly not to try it out while the free upgrade is on offer, but I think that I shall keep my current machines on Windows 7 for as long as is practicable. This is what I did when I was using Windows 2000. Except for having to replace my favourite scanner (since Canon were too mean to provide 64-bit drivers), the eventual move to Windows 7 SR1 was a problem-free experience. Why buy new gloves if your old gloves are perfectly serviceable and fit you like... well, a comfortable pair of old gloves?
Man does not control his own fate. The women in his life do that for him. -- Groucho Marx