Philip Roth's writing style in American Pastoral can be described as maximalist. His diction is potent and energetic, his sentences are long and winding, and his syntax is complex. In addition, the novel is full of historical and literary allusions, a complex intermingling of flashback and foreshadowing, and evocative figurative images.
However, despite the excess and forcefulness of his prose, there's also something meticulous about Roth's writing style. This is evident, for instance, in the impressive balance he achieves between irony and sincerity throughout the novel. While he always seems to treat his characters with a certain ironic distance, he nevertheless depicts their tragedies with seriousness and care. As a result of this, it's not rare for the reader to feel amused and gripped all at once.
In addition, many of Roth's stylistic flourishes can be described as postmodern. This includes his use of unreliable narration and a nonlinear narrative structure, as well as the large amount of allusions which imbue the novel with intertextuality. There's moreover something inherently self-reflexive about the the novel. Telling the story of the narrator's desire to tell a story, the narrative acknowledges itself as a work of fiction within its own fictional world.