I updated to Windows 10 on two machines this morning. The update process was fine, but I've had a few quirks with both systems.
My Blue Iris system:
In-place upgrade from Windows 8.1. After rebooting, I decided I did not like the start menu that is default in Windows 10. So I installed classic shell. This did not work out as I had hoped. Attempting to open the start menu crashed explorer. So I found my way to the control panel and uninstalled it. Rebooted, and reinstalled classic shell. Then it worked fine. No other problems yet.
My main PC:
In-place upgrade from Windows 7. On the first boot after the upgrade, it only detected one of my 3 monitors and would not let me change the monitor's resolution. I chalked this up to the Nvidia graphics driver being out of date, so I downloaded the latest Windows 10 Nvidia driver but it failed to install. I rebooted the system and my monitors were correctly detected. I re-installed the Nvidia driver package and this time it worked fine.
Explorer froze up once, just as I was finishing a Java update. I had to kill explorer.exe and start it again. It could be minor incompatibilities with Classic Shell or DisplayFusion, which I also have instaleld. Hard to say. I am sure this problem, if it continues, will resolve itself within a few months as things get updated.