1. The dual control panels thing has just gotten worse, the new one truly sucking.
2. The lack of sizing/coloring of interface widgets like the windows classic interface allowed. (without hacks)
3. the breaking of ddraw calls for the sake of their dwm (which needn't be the case).
windows 10 has turned into windows 8.1 with a half assed start menu. They still don't get it. I still have to use a half dozen hacks (disableDWM,borderfix), along with a bunch of shims from application compatibility toolkit, to maintain compatibility..and if I want classic interface, I need to use w8classic as well, which creates its own problems.