Trying to think back to my biggest gripes about win 10 vs. win 7 (as Windows 7 was the best OS of all time of course!!) ... would be that I couldn't pin things to a single, simple initial (left-hand) vertical list in the start menu (which in Windows 7 allowed me to access, for example, Paint or Notepad by typing Windows key > down arrow > enter). The other would be the same as many other Microsoft products which have been unfortunately influenced by the Apple paradigm, and that is simply the overall lowering of the owner's ability to customize and reject certain things. There are a few ways to customize Windows updates in Windows 10, but it's paltry compared to previous OS versions of course. I find that repulsive, but Microsoft knows what's best for us.
That said, there are also benefits to simply using what everyone else uses (although I'm afraid that's also the main reason people have Windows 10, while the sellers will of course spin that as validation of its merit).