I found this book to be a bit long and repetitive in parts. And this is from someone who likes to read about language.
The problem for me was perhaps that it read a bit like a text book. David Crystal takes you through all the minor details involved in language, right down to the biological facts of how we make sound.
The more interesting parts dealt with the world's different languages and dialects.
I presume the student of language may find this book more interesting.