Agatha Christie's first book. For that it was very enjoyable. According to Wikipedia she wrote it as part of a challenge to write a book the reader could not spot the perp in. Turns out she did that by making it so obvious that noone ever thought this character could really have done it, and then adding multiple levels of other things that complicate matters.
The book does suffer a bit in other areas: characterization is flat for most of the characters. Sometimes I found it hard to follow who actually was saying what to whom at any given point, despite not usually having this problem. And in the end Poirot and the narrator painstakingly put together the plot in form of a Socratic dialogue stretching over pages and pages while obviously all the other characters in the scene are just sitting there twiddling thumbs.
All in all not a bad read, but justly overshadowed by her later mysteries.