My favorite Hercule Poirot book (if we're talking about Agatha Christie books' I think it's a tie between "Murder on the Orient Express" and "Then there were none"). 
 The book could go on for another 300 pages that I would never guess the ending, and that's what so great about Agatha Christie, she can surprise us without making us feel it's all a too fantastic, unbelievable or just plain impossible - after reading the end I thought to myself that that's just how it needed to end, it couldn't be any other way. 
 If you're thinking if you should read this book let me save you the trouble: just do it! You won't waste your time, there's not a boring moment and the ending is just perfect.