Lethem has proven himself to be a virtuoso of story-telling. His books, for the most part, inhabit a plane of existence that defies much classification, and they wield their creativity with the force of a sledgehammer but the precision of a scalpel. Although his work can sometimes be uneven, it is always entertaining, and certainly never average or boring (to be fair, though, his short stories are hit-and-miss).
This little nugget is, for the most part, a success, but it also comes across as only partially-formed. And although it is, as usual, beautifully and skillfully told, it seems to be less a fully realized tale and more a creative exercise. Lethem, here, is just stretching is literary limbs. Consider listening to a highly touted operatic singer practicing her scales: it's still beautiful singing, and it may even be fun to listen to, but it isn't a song, and there's just not that much to it.