Brilliant dissection of English dialects past, present and future. Found the conclusion a touching rallying cry for diversity against the rising tide of supposedly "proper" vocabulary and pronunciation.
An overall very effective and informative overview/introduction. It's aimed at a general audience, so the treatment of the subject is necessarily somewhat cursory -- cursory, but not inaccurate. (This is especially true where diachronic developments are concerned, which aren't really the focus of the book in any case.) Only occasionally are there passages that I would describe as genuinely slipshod.
I learned a lot. It's a great overview. The prose is not lively, but if one wants the nitty-gritty details about the pronunciation, grammar, and regional distinctions of English dialects -- the precise fundamentals as opposed to perhaps better-written, but fuzzy and impressionistic personal reflections -- then the shortcomings of the prose are readily forgiveable.
Some of my favourite tidbits:
-- the clarification over when "intrusive r" does and does not occur (e.g., "That's a good idea" vs. "the idear is good") -- that where Standard English has "this book" (near) and "that book" (far), some dialects add yet a third distinction (remote), e g. "yon book" -- archaic retentions such as cassn't? ("can't you?") from canst thou not? and ast? ("have you?") from, you guessed it, hast thou? -- dialect words that have no equivalent whatsoever in Standard English: like bracking, "the chipping of eggshells when hatching begins"
And a lot else besides.
(One note of warning: if you know IPA transcription, then you absolutely want the second edition, as the first only contains "orthographic" phonetic representations, which I found to be rather foggy. The second edition wisely incorporates both. )