Hoffman's book, along with the works of Walter Laqueur and Marc Sageman, is the standard text issued to students in the field and to national security officials. It adopts the traditional view prevalent in western academic and military circles: that terrorism is a violent technique employed by non-state actors (mostly Muslims) to achieve political ends. However, even if you agree with such a stance, this work will not help you further your understanding of the subject. In essence, it's a discussion of political theory supported by outdated examples and generalizations; and it fails to provide any practical detailed investigation into the mechanisms of terrorism. Nevertheless, it does possess one important redeeming feature in its authoritative discussion of how terrorists manipulate the media.
The book's first chapter constitutes a poor attempt at defining terrorism. Hoffman does not give his own opinions, but refers instead to definitions published by the Oxford dictionary and several US governmental agencies. He rapidly dismisses the contention that "one man's terrorist is another man's freedom fighter" by arguing that terrorists are not regular combatants because their actions violate the Geneva Convention. More importantly, the book completely fails to address why people might engage in terrorist activities (a subject much better covered by Robert A. Pape's "Dying to Win").
After this introduction, Hoffman presents a brief (and incongruous) historical survey of his subject. In his opinion, terrorism is directly linked to the struggles of post-WWII de-colonization. Like communism, it is an "international conspiracy". This often leads him into the troubled waters of double-standards. For example, he describes Menahem Begin and the Irgun as terrorists during their struggle against the British in Mandate Palestine (e.g. King David Hotel bombing), but does not discuss how this could have influenced Begin's later policies as PM of Israel (the 1982 invasion of Lebanon in particular). Arafat and his PLO are put forward to illustrate the "internationalization" of terrorism (4 pages on the Munich attacks). Yet the reader will search in vain for an assessment of the evidence condemning Israel's war crimes. Treatment of the IP conflict is generally very one-sided. Furthermore, Hoffman's depiction of the Algerian FLN as a terrorist group is far too simplistic. Alistar Horne does a much better job exploring this topic in his masterpiece: "A Savage War of Peace". Overall, one is left with the impression that the author not only picks and chooses his examples, but also fails to properly evaluate them.
There are other fundamental problems underlying Hoffman's analysis. Most of his discussion devoted to the importance of religion in suicide terrorism has been convincingly refuted by Robert A. Pape's research. He tends to ignore the logistical and operational aspects of terrorist groups, and has been overtaken in this field by Marc Sageman (the theory of "sleeper cell" networks). Hoffman's examination of North Africa is obsolete, and there is little or no mention of groups like the GIA, GSPC or AQIM. Informed readers will probably feel that this book is out of date and that current debates surrounding terrorism have moved on.
Despite these numerous drawbacks, Hoffman's introduction to terrorism does produce a very enlightening study of the relationship between terrorists and the media. He is particularly good at using case studies to emphasize how terrorists manipulate television to popularize their cause and recruit new members. This analysis is still pertinent today.
In conclusion, I would say this book is not a good introduction to terrorism. It's superficial, partisan in its approach, and fast becoming obsolete. However, if you are studying the subject, then it's worth acquiring for two reasons. First, because Hoffman is one of the principal academics who represents the traditional, western view in the field. He's a symbol of orthodoxy, and therefore a good source to understand how people think. You'd be daft, however, to let him influence your own conclusions. The other reason is because his work contains important passages on the media's manipulation by terrorist groups. In other words, he's a painful necessity.