This is not one of my favorites, but the idea of it is super. And it made a good TV movie.
It's hard to explain why a person can like this book but still think it isn't very good. I guess it's just that Agatha Christie makes you believe in what she's doing.
The problem isn't plot holes. If you look up this book you'll find people just didn't understand some of it. And well, that's more of a problem, but the real trouble is that most of these people just aren't likeable, and they aren't even really intended to be. I kinda feel like she was trying to say something; a message, about the Bright Young Things in 1932, perhaps.
Redemption in the end is slight. But let me know if you've read it or seen it and don't understand about the hat or watches. I can explain them to you.
Here's the cover of a 1945 edition.