Interesting and dull at the same time (or alternately, I suppose), in a sort of not-quite textbookish way, where if you're vastly interested in the subject then it could be interesting, and yet turn on a dime and bore you to tears on a quite similar subject.
I'm still trying to find a successor to Guy Deutscher's amazing The Unfolding of Language, about how languages change and evolve, so I leapt on Mr. Crystal's subtitle titbit of "words change meaning" and hoped this would be Deutscheresque, but no.
At times he could be quite irritating. Here's a direct quote, easier to read if you know that "FLL" equals Foreign Language Learning:
"FLL is becoming increasingly important as unemployment and reduced working hours add to people’s leisure time. Tourist travel is a major motivation, but many have come to find FLL a satisfying leisure activity in its own right, enabling them to have direct access to the world of foreign cinema, radio and television, vocal music, literature, and the history of ideas."
His point seems to be that if you're bored, having read and watched it all in your first language, a second language opens up new entertainment options. Which is hardly the same thing as "a satisfying leisure activity in its own right," which you could say about model railroad building, gardening, or spying on neighbours. If it's satisying in its own right, don't explain why, that undecuts "in its own right." This sort of writing that would just slightly rub me the wrong way popped up often enough that I thought it deserved mention.
This book really aims to cover it all: from Anatomy to Zulu (a Bantu language). I know a lot about Bantu and other languages because sometimes (often) Crystal moves from precise to pedantic ... it's interesting to learn there are a lot of languages in the world, sometimes spoken by few people. But if I'm never going to remember something (e.g. the number of people who speak such-and-such a language that I never heard of before and will never hear of again) there's no need to tell. Throw in a chart that indicates the relative reach of languages (bar one: # of languages spoken by 1-1000, bar two: # spoken by 1000 - 10,000, etc.) and it sums up the information for you in a way droning on for pages can't do. And I might recall the chart takeaway, but no one (honestly, no one) could possibly assimilate all the information on the various languages, he really lost me there.
And why write a book if those who read it can't possibly remember it? To entertain, I suppose, but this isn't an entertaining book. For future reference, sure (which is why it's textbook like) though thanks to the Internet there are better ways to look up the individual facts. Anyway, intermittently interesting.
There were moments where I wondered if I'd read the book before, some of his examples seemed so familiar, but perhaps they are familiar famous examples to linguists and everyone uses them. Certainly I didn't remember having read the very very dull bits before, so I assume this was my first read.
He also has an English (language) bias, and very much a UK bias, as if he felt assured that only Brits would be reading this book. He'll talk about education, child-rearing, etc., and it's always UK education, UK child-rearing, UK etc., unless he makes a point of differentiating. It's a bit offputting given how many English speakers there are (and he knows how many) to have it presumed all English speakers will be from the same few small islands west of Europe. We're not. I try to just giggle, as when he says mothers reading to their children might mention the "full stop." Not in my part of the world, where we call it a "period," in the unlikely event we point it out to our children (well, maybe baby pointed and asked).
Oh, he's also a bit bossy even when decrying bossy people with their bossy rules. He particularly dislikes it when, say, a Lynne Trusse type will write an exceptionally entertaining and popular book pointing out punctuation issues. He says it's not worth bothering about because those mistakes don't actually confuse people. I'm here to say loud and clear "They confuse me!" I'm terribly literal and don't tolerate ambiguity well, I'm likely neurodiverse in some way. If I see "In the 1970's London was diverse and growing" my brain doesn't automatically rewrite this to "in the 1970s London was diverse and growing," no, my brain expects something like "in the 1970's London was a short-lived market stall" and I grow tense searching for the noun phrase which never comes. It's the same for bad grammar, even aurally, since I also (so much fun) have an auditory discrimination disorder, thus I will always wonder if they did say that or if I just misheard it. So please, world, keep trying to stick to the grammatical, spelling, and punctuation standards, for people like me who need them. (That doesn't make my spelling and punctuation perfect, I'm still human, but I try!)
In summary: I liked it when I liked it, and was bored and irritated when I was bored and irritated.
(Note: I'm a writer, so I suffer when I offer fewer than five stars. But these aren't ratings of quality, they're a subjective account of how much I liked the book: 5* = an unalloyed pleasure from start to finish, 4* = really enjoyed it, 3* = readable but not thrilling, 2* = disappointing, and 1* = hated it.)