Good but too long. Simon and Benjamin (SB) worked at high-ish levels of the Clinton admin on terrorism, and in this book they provide both a historical and policy account of modern terrorism. The book was written mostly before 9/11 and then altered/expanded because of 9/11. This makes it rather sprawling, repetitive, and sometimes unfocused. It really could have been 50-100 pages shorter, and I can only assume that it has scared off some readers with its size. I did find myself saying "ok, you talked about this earlier" many times in this book.
Still, this is one of the clearer explorations of the idea of the "new terrorism" from the 1990s. This was a paradigm shift in terrorism that occurred in the 1990s with the increased blending of fundamentalist religion, apocalypticism, WMD, and mass casualty terrorism (or at least the intention to commit mass casualties). The older paradigm from the 70s and 80s was that terrorists used violence instrumentally; kill ten or twenty or one prominent person to get media attention, leverage, etc. The saying was that terrorists wanted a lot of people watching, not a lot of people dead. However, in the new terrorism, especially in radical Islamist circles, sought out mass casualty attacks (hundreds or thousands dead) for a number of reasons: to fulfill what they saw as divine imperatives to destroy evil-doers, to achieve strategic goals like the ejection of U.S. power from the Middle East, to annihilate a dehumanized, demonic foe, and to fulfill internal fantasies of destructive purification. Aum Shinrikyo, White Power, and Islamist groups like AQ were the harbingers of the new terrorism, and 9/11 was its pinnacle.
SB argue that the US needs a new approach to counterterrorism in the age of new terrorism, but they sketch out a vision of CT quite different from the Bush administration. They are firmly multilateralist, even willing to restrain U.S. power in order to build a wider coalition. They do not see Iraq as closely connected to terrorism, although they see it as a conventional strategic challenge, in contrast to Bush's weak efforts to combine the threats. They see failed states like Sudan or Afghanistan as the real problem or location where terrorism can hide, plot, and expand rather than state sponsors like Iran or Syria, who have more control of their territory and usually don't sponsor mass-casualty, expeditionary terrorism. Overall, this approach to the GWOT probably would have been more restrained and effective than what we got under Bush, especially in Iraq.
A lot of the book is about the roots of Islamic extremism in general and how it transmogrified into various terrorist movements in the late 20th century. SB discuss the impact of Ibn Taymiyya on later thinkers, as well as the importance of ideas like jahiliyya and takfir. I thought these sections were very informative and interesting, although writers like Glenn Robinson cover this ground more effectively and precisely. SB are pretty harsh about the larger context of the Islamic world: they blast the governments and clerical establishments of places like Egypt, Pakistan, and Saudi Arabia for churning out radical propaganda and encouraging Islamist extremism as long as it's directed somewhere other than the ruling regime. They also show the considerable embrace of conspiracy theory and extreme beliefs in the Middle East in general, showing that the extremists are not as much of a fringe as we would like to think. They recommend that the US push for democratization as part of the GWOT in order to create more functional, inclusive states, but to me the experience of the Arab Spring should suggest caution here. What parties are waiting in the wings in these nations to take power? Let's just say they are rarely liberal ones, so we should not deceive ourselves about the most likely alternatives to the current regimes.
While this book is too long and a bit repetitive, it's a solid and mostly interesting look at the evolution of terrorism as well as politics and violence in the Islamic world. It's a bit on the hawkish side, but it's clearly well-informed and not at all prejudiced against Muslims. Recommended if you are a terrorism scholar; if you are just looking for interesting reads on terrorism, try Lawrence Wright or Steve Coll, who are still the gold standards for journalism on modern terrorism.