I bought it when it first came out, and it is still on my bookshelf. A decent book, as the Amazon reviews indicate, but not outstanding.He does cover a lot of ground, introducing emacs programming (and Lisp, in general). I did not find the "Comprehensive Example" chapter implementing a crossword puzzle mode as particularly helpful.
Everyone feels like other people do better negotiating car prices, and I feel the same way about "knowing" emacs. I have used it every day for over twenty years and people are still telling me "there are easier ways to do that in emacs."
Anything that large will have blind spot for a user. Even commiters might be surprised by some kind of idiom in elisp or in a particular mode. That syndrom can be found in languages. It would be of great value to document this side of things. Some spectrum of learning, showing how everybody travels through and that most people go through the same stages. Maybe how to not waste time or feel frustrated by that process.
ps: emacs should have 'didntknowthat...' as subtitle.
pps: I wish for an Emacs rewrite. As a scheme/lambdacalc enthusiast, I love pruning things out to a certain extent, and feel Emacs is too much a bazaar, and would love for it to fork a smaller core mammalian child. Something even more self-documenting [1] and with a stronger fp-ish flavour (when it's not absurd).
The goal, making it easier to learn and understand.
[1] a lot of knowledge about emacs is outside of it both in location (not in the manual) and form (videos, podcasts, static tutorials). This is influenced by the trend for interactive documents (B.Victor, Wolfram) and Notebook/Persistent repls (ipython,...).