For the most part Windows 10 has been pretty stable. Working with as many computers as we do I can say that there are only problems on about 5% of the upgrades, What some people don't realize is that previous windows upgrades were littered with just as many and sometimes even more problems (looking at you Vista).
XP to vista was almost impossible because of driver related issues. Windows 8 had the largest UI change since Microsoft moved away from DOS.
If you are having issues with windows 10 after upgrading ITPRO did a really good write up about most of the issues that we see, If you PC is slow after the upgrade you may have a bad hard drive that was worsened by the upgrade.