Taking a broadly functional approach, as the "How" of the title suggests, the first two thirds of How Languages Work goes through the standard topics, with chapters on phonetics, phonology, morphology, word classes, syntax, semantics, pragmatics, discourse, prosody, sociolinguistics, language change, areal and contact linguistics, and first and second language acquisition. The different styles of the chapter authors remain apparent, but there's been comprehensive editing to make the book a nicely integrated whole. Some material is broken out into sidebars and textboxes, but not with distracting frequency. The pedagogical material is not overwhelming either: each chapter includes brief "Key Terms", "Chapter Summary" and "Suggested Further Reading" sections, as well as more extensive exercise sets; there are some online resources as well.
The "Languages" in the title is given a lot more than token acknowledgement. English is used for most examples, but other languages appear throughout — Atsuwegi verb roots, for example, illustrating cross-linguistic differences in how motion events are framed. And the International Phonetic Alphabet is introduced right at the beginning, but language-specific transcription systems are used where appropriate. On top of this, the last third of How Languages Work offers thirteen "Language Profiles". These provide some background on the language and its speakers, and collectively illustrate something of the world's linguistic diversity, but are not general language profiles. Instead they focus on particular features of interest, such as Kabardian phonetics and phonology, South Conchucos Quechua word formation, and Indonesian spelling reform. Concrete examples are given for the features discussed, and the language profiles also have exercise sets.
How Languages Work would, I think, make an excellent textbook: anyone working through all the exercises, instead of just dabbling in them as I did, should come away with a pretty solid grounding in the subject. It is amenable to a less involved reading, however, and never feels dry or lacks motivation: anyone with a bit of curiosity about linguistics should go away more excited about it.