I have read through about 2/3 of the TeXbook so far and currently am writing my thesis in it. So far it's been really enjoyable! That's not something I could say about my past struggles with LaTeX.
Maybe once I have TeX down really pat, I'll peek back over into LaTeX, but for now I really don't see a need.
Getting a handle on the typographic primitives that TeX offers makes a huge difference. I've actually found it surprisingly easy to handcraft whatever macros I need. Though I do also use a the amstex macros.
Admittedly, it's easy to end up with a horrid mess of macros if you're not careful, but a bit of forethought and experience with frontend design patterns goes a long way.
One thing I haven't figured out yet is how to deal with CJK languages nicely.
Deckset is cool but I can't customize much of the layout, and I don't love HTML-based solutions. I don't love Beamer either because you have to write a lot of ceremony for a single slide, and most styles feel very "old" (lots of side/top bars).
Here's an example of what you can do using the `lecturer` package:
https://twitter.com/evacchi/status/738018829905887232
the only problem with plain TeX is that there is no good listings package