BY DEFAULT HIDE FILE EXTENSIONS!
I always thought that was one of the stupidest decisions in the entire history of software... and I can't believe they are still doing it after almost 20 years.
e.g., There are 5 files named "setup"... which one is the executable? You have to go by the tiny, inscrutable icons.
Of course, hiding the file extensions of Office files didn't do much back in the day when Office should have been known as the Microsoft Virus Development Kit, but at least that has gotten a lot better.
I think the biggest arrogance of Windows 8, aside of foisting Metro on you whether you want it or not (you don't, and even if you did, all the Metro apps take 10-20 seconds to load.. is this 1989?) is that you cannot go back to the "classic" UI theme, which is, in my opinion, the last UI theme Microsoft made that wasn't hideous. XP had that awful "Playskool" theme, Vista was only slightly less ugly, but also had epilepsy-inducing animations. Windows 7 was a bit better. At least you could choose a color theme that didn't look like it was made by a color-blind mental patient. But in all cases, you could go back to the "classic" look, which was always slimmer and more efficient. Now you can't because either Windows is no longer capable of displaying it, or because they simply think that this hideous and ridiculous "flat UI" fad is so good that no one should be allowed to turn it off. "Flat UI" may be OK for a phone, but for a desktop environment, it's a huge step backwards, but it's not just limited to Metro. You have the stupid flat look on the desktop as well.
Windows 8 is the biggest exercise in user-hostility in the entire history of non-enterprise software. In the world of enterprise software, it's not bad at all, but that's because enterprise software is usually about as user-friendly as the Soviet bureaucracy.