I didn't know this was a postmodern novel until I was halfway in. So I only started to understand what the novel was about after I'd read half of it. Spark's novel is about a bunch of Swiss servants staging the death of their master so they will inhert the estate. There is zero suspense over whether the plan will succeed. It's pretty much preordained, and more like a satire, an intellectual game about parodying fiction. I feel like the novel is meant to be approached as a literary critic, not a reader.
There's also a lot of dialogue - most of the novel is dialogue which resembles the play or screenplay format. Dialogue which is hard to follow because characters resemble ones from an Ayn Rand novel, ie they are cardboard cutouts, making it even more confusing and hard to remember who is who among the large cast. The speakers blur into one another because of their lack of psychological (or physical!) differences, leaving the reader wandering in Silent Hill fog.
I also read Juan Rulfo's Pedro Paramo recently, and enjoyed it much more, despite it having a similarly confusing dialogue syntax, not signposting which character is speaking and takes on an intentionally fragmented structure. Perhaps having memorable characters helps the poor reader's memory.
Let's use the principle of charity and argue that the cardboardness or cardboardity of the characters are to draw attention the mimetic quality of the novel and hence form a stronger critique on literature. I still don't enjoy it. I think if you're publishing a postmodern novel you should paste a big sticker on the novel cover saying "POSTMODERN NOVEL" to prevent all the headaches and suffering.
This one is for the Pynchon and Wallace enjoyers, the bourgeoisie intellectuals, not this humble subaltern.