Perhaps aesthetic - both Windows 1.0 and 2.0 were (to me at least) very ugly. Things got a bit better with Windows 3.0 and 3.1 (and easier to program) but it wasn't really until Windows 95 that the whole thing came together. One thing you have to give Microsoft (at least back then) is that they did keep trying. And, speaking as a Windows developer, their documentation was very good.
> it wasn't really until Windows 95 that the whole thing came together.
I remember the launch parties for 95. I remember thinking to myself how strange it was to go to all of that expense to promote an OS.