Lisa Jardine's main thesis - that his assassination was an historical turning-point - isholed at the start. Elizabeth did send troops to the Netherlands in 1585, but that was because her policy of keeping Spain and France at each other's throats had failed.
Nor is it true that William's assassination triggered the 1588 launch of the Spanish Armada. Many more factors were involved, not least the execution of Mary, Queen of Scots, and the depredations of Drake in the Caribbean and Spanish America. The thesis that William's murder changed European history doesn't really work.
Set that to one side, and it cannot be denied that Jardine spins much ingenious material out of this conceit. She argues, correctly, that the advent of the handgun held terrible consequences for rulers. Elizabeth was thrown into a panic at the thought that such a weapon could harm her godlike person. There is good technical discussion about 16th-century pistols, and a horrific bit on the tortures visited on William's killer, Balthasar Gérarda, a 25-year-old Catholic lone assassin.
Of all the famous assassinations, perhaps only those of Franz Ferdinand in 1914 and Julius Caesar in 44BC changed world history; not even the murders of Lincoln and JFK managed that.
However, Jardine's book is a refreshing foray into an area often neglected by historians, and her enthusiasm makes one overlook hyperbole in her claims.