As it's written by someone who has been closely related to Hadrian's Wall, the book, probably not surprisingly, seems to concentrate on the forts related to the wall. A more balanced assessment of the forts in Britain would have improved the book. No complaints about delivery.
My version of this book was produced by English Heritage in 1997 and covers 120 pages of their large format (roughly A4) publications. Chapter headings include plans and functions, buildings, outside the fort, supply trade and industry, and the end of Roman forts.
It seems that Romanists define legionary bases such as at York and Chester as "fortresses", and the much smaller auxiliary defences as "forts", so while this book mentions the larger fortresses in passing, it's mostly about auxiliary forts such as those on Hadrian's Wall.
Some questions in Roman studies don't seem to admit of a simple answer, and opinion swings back and forth like a pendulum. Were the Saxon Shore forts such as Portchester built to defend Roman Britain from Saxon pirates, or were they built to defend a break-away Britannia from Rome itself? In the later period, did the forts on Hadrian's Wall take in families from the surrounding settlements, and morph into fortified towns of peasant militia, or is this to read too much into too little evidence? Bidwell does not always come up with firm answers, but at least he states the questions.
There are also plenty of less contentious areas where the book is informative and well illustrated, with 8 colour plates and 80 black and white diagrams or drawings. Some of the diagrams are poorly described, for example, diagram 44 shows an arch to the left which is described in the text as being to the right. This does not prevent the book being a worth-while read for people interested in this subject.
If you enjoy this book you will probably like the free on-line futurelearn course on Hadrian's Wall.