An upgrade to Windows 10 is going to have problems. To get a full 10 installation, you need to run a clean install.
Now, since that's out of the way, once you disable the tracking on Windows 10 I feel like it is a great system.
Much of the features disabled by tracking programs are the 'automatic updates' and the like.
After a Classic-Shell installation, it feels like Windows 7 that runs faster, but there are a few programs that now refuse to run (e.x. 3Ds World Studio) however they are all extremely dated anyways. I've had a driver issue with a few things, but they were all fixed by selecting the correct driver from the list of drivers. I have broken my installation enough I don't know if Cortana or the search work, but the shell file search is working fine and that's all I need.
My PC is on a TV. The very edges of the tv are impossible to see where I sit. Windows 10 uses a small bar on the taskbar to indicate open programs. I cannot see the bar at the bottom of the taskbar so I had to move the taskbar to the top of my screen. If you can't see the edges of your TV/Monitor very well you will have problems as the indicator is very small.
Nutshell: Windows 10 is a great OS IF you perform a clean install and optionally remove privacy invasive features using a program like DoNotTrack10.