I agree with Howard about the control panel. The control panel as on windows 7 is much more powerful. It's also where you can configure practically anything (along with mmc). The new app with windows 10 is only for guys who want to set up the basic things. This split is just annoying.
Another point: the new look & feel of Windows 8/10. Sorry, the GUI is not beautiful. Everything's flat, without relief, with basic colors and themes. I have the the impression to be back to Windows . Microsoft, please, have a look at OSX. If Microsoft wants to be successful, the GUI has to be as nice as OSX.