I'm at pg.40, 15% into the book, at the part just after The Voice had spoken (wow, holy shit here we go!).
I'm also having trouble with the huge cast of characters, but I'm able to manage it better slowly as I go along. It was a very elementary introduction and none of the characters feel at all sufficiently fleshed out, but I suppose that if they're introduced enough for the purpose of the mystery/thriller aspect (which the story is known for), then it should be all good as long as that aspect of the book is executed perfectly.
Minor gripe: I feel like the dialogue is written in a very clunky manner. I'm not sure if it's just my copy, but in other novels I would always see dialogue written in the following manner...
"Owen? Did you say Owen?" she said sharply.
instead of Agatha Christie's format...
She said sharply:
"Owen? Did you say Owen?"
It just comes across awkwardly.
Also: The adverbs! Maybe I'm more particular since I just finished Stephen King's On Writing, which pretty much admonishes the use of adverbs (and is backed up by William Strunk, Jr.'s The Elements of Style) - but holy cow, Agatha Christie showers adverbs on her dialogue attribution like a 5-year old would put chocolate sprinkles on vanilla ice cream.