The narrator and his girlfriend in The King Of Sentences, the second story in Jonathan Lethem's occasionally frustrating new collection, are bookish obsessives. They have reduced the world's literature to a pantheon of one, the titular king, delighting in the beauty of his language when, as a minatory encounter with him makes ambiguously clear, they really should have paid attention to what he was saying as much as how he was saying it.

This tension, the profitable opposition between form and content, as well as his rarely overbearing self-consciousness, is what makes Lethem such a pleasure to read. In his superb 2012 essay collection, The Ecstasy Of Influence, which offered a tour along the capacious highways of his interests and aesthetics, he wrote about his unabashed obsession with what might be considered more marginal forms, like comic books and science fiction. Skilfully receptive both to the potential of this cross-genre pollination and to the fracturing blizzard of the media environment that makes it possible, Lethem generally manages to avoid reducing his work to mere pastiche or to no more than a trite checklist of pop-cultural references.

In the shorter form though, his writing often risks seeming more like an exercise or an enthusiastic riff on a new theme. In this collection, Their Back Pages, where a collection of comic book characters are jettisoned from their panels and marooned on a desert island, is a thin idea stretched too far, and The Dreaming Jaw, The Salivating Ear, a mock-heroic authorial defence of a blogsite under attack from an internet troll, doesn't in any way justify its 13 pages in what is, after all, a slender volume. Whimsical and doodling, these two stories end up as the worst (or best) exemplars of the more vacuous side of American postmodernism.

Fortunately, the remaining pieces demonstrate Lethem at his considerable best, ranging from the snappy and surprisingly sad New York anecdotalism of the title story, to the haunting and blackly comic Procedure In Plain Air. This is a Kafkasesque fable of arbitrariness and complicity, where a bystander outside his local coffee shop watches in near-passive distress as a cowed and traumatised young black man is sealed up in a hole in the ground, freshly excavated by a work crew of jumpsuited guards.

Like the other American writers with whom he could be grouped – Michael Chabon, Jeffrey Eugenides, David Foster Wallace – Lethem takes great moral and rhetorical pleasure in the precision of his language, as well as in its destabilisation. Pending Vegan wrings real comedy not just from its depiction of the main character's psychological travails, dwelling on his secret although so far unfulfilled identity as a vegan during a family trip to SeaWorld, but also from its exactness of phrase: the orcas, for example, "like panda bears redesigned by Albert Speer".

In contrast, Traveler Home, an extraordinary story about a pack of wolves delivering a newborn baby to a man who has recently moved to the country, is written in a kind of compressed, primal poetry, perhaps linguistically replicating the Germanic fairytale it so clearly resembles by frequently placing the verb at the end of the sentence. A scene as mundane as the main character knocking the ice from his satellite dish after his TV picture breaks up becomes as incantatory as Beowulf: "Through own window like yeti peeper, Traveler spots lit screen, image rescued."

The leaven in the bread of these stories is an engaged acknowledgement of American decline, and the way rampant materialism seems increasingly unable to paper over the cracks in American society and culture: the loathsome hipster café in Procedure In Plain Air, where the main character puts off job hunting for another day, is full of fickle "overdressed-disheveled types, nerve-wrackedly Web-surfing"; Kromer, the main character in The Porn Critic, works at a "painstakingly derived" shop called Sex Machines, where, with feeble, desaturated irony, he writes in-depth staff reviews of porn films that the customers will never read.

Although a slightly unbalanced collection, dragged down on one side by the dead weight of Their Back Pages and The Dreaming Jaw…, buoyed up on the other by some effervescent ideas and phrases, this is on the whole a solid introduction to a writer who is not only playful and ambitious in his use of genre and language, but who is also, when on best form, a pure joy to read.