Really great puzzle book (or rather books, since this is a 3-in-1 collection). All the pages have gorgeous full-colour illustrations and there's a story tying together everything. Not sure what the recommended reading age would be, though -- I'm an adult and quite good at this kind of stuff, and it still took me about a week to get through every puzzle.
Overall I think my favourite is the first book, Maps and Mazes; the story is the most convoluted and the amount of details is simply amazing. Unfortunately, the book doesn't provide a solution for the final puzzle, and for the life of me I can't seem to find the 8th clue that would enable me to find the stupid Rock of Plot Point.
The second book, Codes and Cyphers, is the easiest to solve. All the codes are explained so one only needs to read the instructions and patiently decode the messages. There's literally no way to get stumped. But it's still satisfactory to put four passcodes and four cyphers to decode the final puzzle.
I'm rather lukewarm towards the third book, Logic Puzzles, because I've only just discovered a mistake in the final puzzle, two symbols have been switched around and it's impossible to solve. This book just doesn't seem to have been edited as carefully as the others, sometimes the puzzles are only difficult because the meaning of the text isn't clear, and I'm convinced that at least one other puzzle has multiple solutions.
Despite those niggles it's the best puzzle book I ever read in twenty years of avid puzzle-solving. Oh, and one of my favourite things: the book is absolutely full of female characters. None of that boys-only-adventure-club bullpoop.