Israeli's book reads more like an attempt to cash in on interest in the Islamic State than a serious investigation into the phenomenon. Besides being a re-articulation of the author's own prejudices (e.g., there is no such thing as "moderate Islam"), much of the book comprises rambling disquisitions that provide no insight into the Islamic State; long paraphrases of single articles written and published by others; precious little by way of citations to support his arguments, and virtually no engagement of primary sources in Arabic.
On the subject of the Islamic State, basic errors immediately arise. Ansar al-Shari'a in Libya is aligned with al-Qaeda, and has not pledged allegiance to the Islamic State. The Islamic State did not begin "as a subordinate to [Syrian-based] Jabhat al-Nusra in early 2011." In fact, what was then "the Islamic State of Iraq" played a primary role in establishing Jabhat al-Nusra by dispatching operatives into Syria in mid-2011 with weapons and financial support. Considering that Israeli discusses Nigerian-based Boko Haram at some length, his lack of awareness that the terror group pledged allegiance to the Islamic State in March 2015 is baffling.
Stylistically, the book suffers from repetition of content and could have benefited greatly from an editor's clarifying red pen: In a discussion of the Muslim Brotherhood in Egypt, for example, several sentences suggest Mohamed Morsi is still president despite the author's also referring to his overthrow in the July 2013 coup.
This is not the book for readers looking for a good summary of ISIS's global dimensions.