This is a really interesting book, and manages to be both representative of Christie's work and something very different from most of her books - simultaneously.
I have marked this review with a spoiler tag, because, although I don't intend to provide a play-by-play of the book, I will reveal a pretty important plot device that, if you haven't read this one and you are a fan of Christie, you shouldn't have revealed.
Let me say here, so I can get it out of the way, this book is well worth reading for fans of Dame Agatha. It is outside of her series - Hercule Poirot makes no appearance, nor Inspector Japp, Miss Marple, Colonel Hastings, or Tommy and Tuppence. This is 100% stand-alone. So, if you are a Christie fan, stop reading, track down this book, and read it.
Then come back and tell me what you thought!
In terms of the similarities, well, it's set in the same sort of place as most of her other books. It is a piece of domestic fiction, with descriptions of houses and rooms and British life that are consistent across most of Christie's books. The characterizations are pretty standard early twentieth century British. It was published in 1967, but honestly, it could have been set in the '20s through '40s, which are the time periods that I most associate with her books. It bore a strong similarity - plotwise - to Death on the Nile, which is one of my favorite Christie novels.
In terms of differences, though, it is a barely a mystery. It is much closer to a thriller, and represents one of a few forays by Christie into using an unreliable narrator. And it worked beautifully - I can be pretty ambivalent about this particular plot device. I liked it here.
I called it pretty early, though, within the first 25% of the book.
This book was under the tree for my daughter. She is a huge Agatha Christie fan, and this is one I don't already own. It is also one of Dame Agatha's ten favorites, along with Murder on the Orient Express, And Then There Were None and Crooked House (which was also under the tree for the girl, actually). She was completely blind-sided by the ending - she is a less sophisticated suspicious reader than I am, apparently.
Anyway, it's good. You should read it!