Why did I love this book?
This book is out to trick you. It presents itself as a compendium of charming puzzles and brain teasers that will make you scratch your head until you suddenly yell “Aha!”. But far greater trickery lies ahead, because these riddles are devilishly constructed to lead you --- with no additional effort --- to the most profound discovery in the history of mathematical logic. That discovery is Godel’s Incompleteness Theorem, which says that mathematics (and indeed even just arithmetic) defies logical description and therefore transcends mere logic. There are more things in heaven and earth than are dreamt of in your logical reasoning.
You could understand Godel’s Theorem by reading Godel, but that’s hard. Reading Smullyan is easy. It’s better than easy; it feels like playing a wonderful game against a bright and very funny opponent.
As a side note, this was the book that inspired me, decades after I’d read it, to imagine that I could teach economics through a series of brain teasers in my own book, Can You Outsmart an Economist? Smullyan died just as that book came out. I wish I could have sent him a copy.