Anyone who has only ever used LaTeX will be pleasantly surprised by plain TeX - so many of the things that you'd think must be LaTeX macros are actually just TeX itself.
The downside is that once you know, you know and you will see lots of bad typography. Though I genuinely think digital typography has continually and gradually improved over the decades. The typography you get "out of the box" is much better than 20 years ago. Also, high dpi displays rock!