I was aware that the discourse is different between disciplines and that each discipline has its own unique requirements.
Book reviews also provide the historian with a thumbnail sketch of the contents - that may be very useful in research work.
Writing a book review requires that you assess the books strengths and weaknesses as they pertain to historiography - it is not a literary review.
History students are expected to learn the discipline: to become historians.
In order to review a book on history it is essential to have some information on the subject, the region, and the period.
The points you raise (both positive and negative) need to be supported with evidence just as for other forms of academic writing.
Write some questions based on the list above: Locate some other sources on the same content/issue and/or the same genre to provide you with background and other views.
Pay attention to introduction and preface as this is where authors often present the reasons for their book, their perspective and those of any other contributors. This gives you a quick overview of the contents; looking at any pictures/diagrams, tables/graphs, in the chapters shows you some of the strategies the author has used to get the meaning across.
These contents may give a clearer indication of the intended audience as well.
The historical source under review is usually secondary, that is, it is about an event in history that the author has contributed some new information.
The review is critical in that it discusses and evaluates the significance of this new information.