You can't change the window title bar inactive color, or change the size of borders (and yes I use these features). Lack of colors to choose for the window title bar, only about 40 different colors. Can't individually adjust the text and colors of text of various UI elements, which results in some issues of black text on dark colors or white text on light colors. In Windows Explorer they removed (or simply didn't add it back in) the function that when you select multiple items and then change sorting your selection is lost. They also removed the free disk space indicator on the status bar (and don't say it confused users, it had to be manually enabled). Granted I know these are somewhat small things but they are advanced settings that advanced users liked to change. Why remove customization?
And in general I feel the newer interface elements aren't complete, particularly with control panel items. Some stuff is the new style GUI, yet a lot of it still can only be done for the old. It is a messy mix of settings in both new and old UI's and it is confusing and frustrating. And in addition to that the new interface doesn't allow double-click the left side of the title bar where the Windows 3.x and earlier versions had to close the window. This still exists in the old UI based applications but not in the new "metro" UI applications. I'm sure a lot of people didn't even know about it but again, some of us advanced users still used that feature to this day. All of these little things add up to wasting time trying to customize your computer to your liking so you could get work done quickly and efficiently. Windows used to be all about customization, you could set it up pretty much however you wanted. It is starting to become like MacOS, with everything locked down and limited features, and you can only do things the M$ way. Pisses me off.
While yes games are as far as I'm aware performing better in Windows 10, Windows 7 is still no slouch. We still have a few years before DX12 games require us to move to 10. In the interim I'm going to kick and scream in an effort to get M$ to give us back the customization that made Windows such a great OS. Right now, the benefits of W10 do not outweigh the benefits of W7.