I got to boot a Pentium III desktop (Dell Dimension XPS 1450) few monthes ago. I missed nothing about today's UX. It was no brainer yet not restricting for 90% of your needs. Extremely light and fast (the whole OS runs in less memory than an average webpage). I almost tried to build emacs and a scheme and live in heaven forever.
There was a classical canonical sweet spot in this era design mindset. Kinda like going into a country side cabin. No fancy stuffy, yet most things are just like they need to.
ps: It's hard to remove nostalgia / habit bias; but I consider myself far from prejudiced, having gone into almost all UX fads since I had a keyboard and a mouse. I accept qualities in all systems be it Apple, Linux, Amiga, SGI, HP handeld calcs and all kinds of different ergonomics (CAD, Compositing, Video, Audio, code, shell, IDEs, Smalltalk) ... And even after seeing all of this, Old Windows (until 2K) had a nice sweet spot feel.