I bought this as a stocking filler present but have ended up reading the entire book myself (cover to cover in one long sitting, I couldn't put it down). I don't write many book reviews but had to here, and I was enthralled by a thought provoking, engaging and intellectual riddle book; not at all a silly tea-time quiz book.
The puzzles are grouped into sections: "Logic & Probability", "When Reasoning Goes Wrong", "The Real World", "Motion, Infinity & Vagueness", "Philosophical Conundrums" and "Paradoxical All The Way Down" (i.e. stuff with no solution - yet). In each section there are quick fun quizzes you can read out, and also longer riddles which usually exemplify a well known (in mathematical or philosophical worlds) problem.
In the back, the solution to the problem is very clearly explained with examples and diagrams and, most interestingly for me, the historical or real-life context. For example: that Simpson's Paradox was demonstrated in and brought down a court case in 1973; that Sorites Paradox was first posed 2,000 years ago; or that a game destroyed 30 years of work or a well-known mathematician. From this I was able to further research things that interested me.
You might recognise some famous concepts (whether by name or not) such as the Prisoner's Dilemma, the Paradox of Deterrence (i.e. should we engage in arms races), which mystery box to pick in a gameshow (based on probability theory), and it hints at concepts I vaguely recall from my degree-level maths (concepts of infinity demonstrated by guests in a hotel, set theory demonstrated by a librarian cataloging books). There is also "The Gambler's Mistake" that Derren Brown recently used on TV (but this book is not nearly as annoying as him).
If you are have even a slight interest in fun maths or philospohy, this book is a great light but interesting read, even if you don't actually want to attempt the puzzles but flip straight to the answers at the back. However the complex stuff is only hinted at and the whole book is short, concise and fun. My whole (non-nerdy) family enjoyed dipping into these puzzles. The book gives you hints for approaching a solution and the solutions are very clearly explained - with digrams, examples, and real-life application. (As a hint for approaching Einstein's riddle, I suggest drawing an even bigger table with all possible options along each side and marking/crossing off combinations as you go.)
As a present, the book is slim but feels good quality with 144 glossy, neatly laid out pages, with nice pictures here and there. I also found the author very humorous, which makes the book more engaging still.