The prose is a delight to read and its scope is downright inspiring despite its relative brevity.

This is of course one major reason for the longevity of Elliott's work despite its relative age. There are also other factors that have made Imperial Spain one of the introductory texts for Hapsburg Spain.

For one thing, Elliot intended the book to be a textbook from the start. He wrote it while researching and writing The Revolt of the Catalans and discovered that there were no textbooks on Spain, so he wrote one to meet this need. Prior to this time, most Anglophone histories of Spain tended to approach Spanish history from either a sectarianism teleology emphasizing the retrograde nature of Spanish Catholic society or recapitulating the Black Legend of Spanish absolutism and obscurantism. Elliot, taking a cue from Ferdinand Braudel, instead looked at structural factors as the source of Spanish decline. Imperial Spain emphasized that the Hapsburgs suffered from an overstretch imperial aims outmatched the empire's grasp. Yet Elliott departed from Braudel in an important aspect in that the former emphasized how individuals perceived decline and tried to manage decline. Braudel's Annalles style history is often quite bloodless and places far less emphasis upon the role of individuals.

This was a very novel approach to both Spanish and European history when it was published in 1963. Elliott himself notes in his autobiography that he was fortuitous to historicizing imperial decline in 1963; the British Empire possessed its last trappings and America had started Vietnam. He tapped into a wider historiographic tradition of the rise and fall of empires exemplified by Gibbon, but Elliott was using what was at the time a modern historical methodology rather than falling back upon essentialist interpretations.

The Elliott overstretch thesis is also one that is quite durable. It has the virtue of being relatively simple and provable. Few historians question the fact of Spanish decline. Spain at the end of the seventeenth century was by most indices far less powerful than it was the century prior and many contemporaries knew commentated upon it. Overstretch also has the benefit of being a useful paradigm in political commentary. For example, Googling "Imperial Overstretch" leads to a lot of political commentary about foreign policy. In this case, Elliott backs up this line of thinking.

Overall, historians of Hapsburg Spain tend to agree with Elliott more than they disagree. There is of course a wide corpus of social history that has been written since 1963. One blind area of Imperial Spain is there is little on gender, of which there has been much written on in the last decades. It is a tad unfair to critique Elliott for not incorporating gender history though when the concept of it was only in its nascent forms. Most of where Elliott is superseded or qualified has to do with the nature of imperial decline. Jan Glete, for instance, argues that Elliott overstated the gulf between the Hapsburg center and its imperial periphery. Economic historians have also countered some of Elliott's picture of the Spanish economic decline, albeit keeping to the same contours as Elliott. The strongest direct critique of Elliott comes from Henry Kamen, who argues that far from declining, Spain never rose. Kamen argues that the brief period of Spanish hegemony came from an artificial constellation of the Hapsburgs being in the right place, the misfortune of the French Valois, and the rise of sectarian Protestantism.