This is slow going. The pages feel dense and the way Updike writes forces you to concentrate. Through his descriptions of the landscape, buildings and interiors he is making a statement about the state of Kennedy's America compared to the past.
As the new couple, Foxy and Ken, start to get dragged into the world of the couples an attitude to life where people try to get away with pleasing themselves as much as possible starts to be detailed in greater depth. The central character Piet seems to have time to see his mistress, construct hamster cages and plan his social life as well as keep down a job as a builder/developer.
his inability to see how fortunate he is feels like a point being made by Updike and presumably Piet's life seemed as self-indulgent when this was first written as it does now, particularly in a time of recession.
One of the main struggles you suspect as the first 100 pages gets passed is trying to attach any likeability to any of the couples. So far none of them appear to be the sort of people you would go out of your way to meet. Again that is the point but it is going to be a challenge.