Though published in 1988, there are a few outdated suppositions that throw the whole book into imperfection--that "pen" is quickly lapsing into obscurity, that "queer," "fairy," and "fag" have been entirely replaced by "gay." The focus on British English with only a few passing (sometimes imprecise) references to the other side of the ocean wasn't something I particularly loved either, nor the judgmental criticisms of modern English's fluidity (that words can playfully take on other parts of speech, verbs morphing into nouns and so forth)--there's a condemnation of the fluidity with no respect for its playful cleverness.
Anyway, aside from those personal setbacks, I enjoyed the book. The text is interesting and well-informed, particularly the analysis of Caxton's registers, Chaucer's dialects, Shakespeare's coinages, of Anglo-Saxon vs. Norman vs. Greek/Latin roots, of the secularization of church words, and of prominent uses of propaganda (notably surrounding the Church of England).