This most excellently written work covers a very large amount of research done on politeness in the linguistic field since the beginning of the study. I would recommend it to anyone interested and/or working in and/or on politeness as a linguistic object.
The only reason why I didn't give it 5 stars was because if you're not familiar with the many theories dealt with in this book, you may get somewhat confused, not that Watts fails to expose them in their essentials, but because it makes tons more sense when you actually know the theories beforehand. However, most of the book is readable even for people who haven't spent ages studying linguistics, though I would not recommend it for someone who doesn't know a thing about linguistics. Naturally, this isn't a work of vulgarisation so it shouldn't be expected to be so widely accessible, therefore yes, maybe I should give it 5 stars. But the thing is, I'm supposedly knowledgeable in linguistics (somewhat) and I still had some difficulty getting everything with adequate comprehension.
Certainly a classic in the field, nevertheless.