Nostalgic, Angry, Ambiguous, Mischievous
Blood may be thicker than water, but nostalgia is thicker than freaking molasses in American Pastoral.
The nostalgia running through American Pastoral—nostalgia in the sense of looking back with longing on an ideal past—is interwoven with lots of anger. This is anger at the parts of the past that aren't so ideal, and anger that nothing can ever be as good again:
The war-crimes trials were cleansing the earth of its devils once and for all. Atomic powers were ours alone. (2.1)
This is an angry quote masquerading as a nostalgic one—Zuckerman is remembering the exuberance of the late 1940s in America and how deluded that happiness was. After all, as the Cold War would show, atomic powers were not America's alone. And certainly the devils of the world were alive and well… and some (especially according to Merry) were in the dang White House.
We leave it to the readers to decide where all this anger is directed—is it at the Vietnam War? Other historical events? At the Swede? Other characters? All of the above? There are so many choices, and so many positions explored in the novel that it is ambiguously open to many interpretations. Philip Roth's books usually provoke controversy, dialogue, and strong emotions and this one is no exception.
For example, Richard Edar, in his review for the Los Angeles Times, accuses Roth of projecting an anti-assimilationist fantasy—that Roth is using Zuckerman (and Zuckerman using the Swede) to criticize and even punish Jewish people (like the Swede) who have assimilated, or blended, into "mainstream" US culture, and who have married non-Jewish women (shiksas!). Edar argues:
In "Pastoral," Zuckerman tugs on a glove-puppet of his own. Unlike Roth's glove (Zuckerman himself), his cannot withstand the gesticulatory passion of the hand that wields it. It keeps ripping. In fact, Zuckerman's puppet—a well-meaning, idealistic, assimilated Jew named Seymour Levov—is mounted precisely for the purpose of being ripped. (Source)
Alternatively, Michiko Kakutani of the New York Times suggests that Roth has a tone of tenderness toward the Swede and his story:
[…] a kind, forbearing man who unexpectedly finds himself chewed up and spit out by the noisy machinery of history. […] [T]he Swede's decency [is] palpable—and yes, compelling […]. Seymour, we realize, is the quintessential innocent, a man whose life has broken into a Before and After, a man who finds himself trapped between the moral certainties of his father and the angry denunciations of his daughter. (Source)
In addition to nostalgia, anger, and ambiguity, there is a definite tone of signature Rothian mischief. Whatever other points are being made, some mischief is behind Jerry's hamster skin coat, and even Lou Levov's final forking, to point to two of many outrageous moments. Even when Roth writes a book as serious as this one, the merry prankster who brought us the infamous Portnoy's Complaint can be seen spicing things up.