It's generally less "rule discovery" and more "paper puzzle" than LOK and Abdec. Smooth difficulty curve, but ultimately ends up pretty challenging.

The 100-ish puzzles in this book are almost all small puzzles where you can figure out in 10 mins to half an hour, but it doesn't need to be "Logic Masters" type difficult to explore fun ideas of the novel puzzle system it created. It successfully condensed the "essense of fun" of doing paper puzzles IMO - using non-trivial observations and deductions to break a seemingly impossible puzzle wide open - while still being approachable even to players that are not experienced in paper puzzles.

Another masterpiece from Letibus Design. Highly recommended.