Honestly? I've had little trouble with Windows 10 itself. It runs remarkably, faster booting up, nice and clean setup, etc.
My problem lies with UPDATES to Windows 10. Truly, updates are important and necessary for the company dishing them out to make sure their security and what not is up to code. However, it seems like every time there's an update for Windows 10, I have nothing but issues for the next untold amount of days. (Usually a follow up patch update fixes the problems I'm experiencing, but this one was an exception. I do not know if it is because the issue occurring was not covered in the patch or what.)
After the most recent update, it seems like I have to hard reboot my computer, by holding the power button for 8 seconds, anywhere between 2 and 5 times. Why? Because most of the time my computer freezes while booting up.
Other than the obviously stated concern, I have no problems with Windows 10.