Well, you are bound to have some books that aren’t as good in any long running series. I am quite obsessed with all things Poirot but Dead Man’s Folly wasn’t up to the same caliber as most earlier installments. I’ve read that Christie became either bored or frustrated with the character and, in some ways, you can see it in DMF. For me, the series is at its’ best in the books written from the 20’s to 40’s. This book, written in 1956, doesn’t have the same feel.
Without going into too many details, part of the issue is that most of the police investigation takes place with Poirot off the scene (and therefore, the page). It’s hard to understand how or why he would solve the mystery when he wasn’t there for many interviews, etc. Also, the ending was fairly preposterous. This was no red herring or plot twist. It just didn’t make sense really.
Having said that, I do enjoy Ariadne Oliver as a secondary character. And, I believe David Suchet narrated the audio for this book. I may choose to listen to it in the future.