I am reviewing a complete software package that has a base OS, UI, file explorer, browser, etc. As an every day user I don't care if they tweaked handling device drivers that crash or made memory usage 2% more efficient. Do I want those, sure, but they fall into the list that you expect to just work.
The UI is what I interact with every day. Did the screw with it more in a good way or a bad way? That is what everyone wanted to know and why so many people installed it.