A good number of easy and medium ones to start off with, then difficult ones to enjoy and solve. Then there are the fiendish ones to really satisfy when the 'urge' kicks in--not so tough that you need a computer to solve, yet challenging enough to take half hour, fair bit of concentration, some pencil markings, some head-scratching...then voila, the EUREKA moment!
Oh, the four stars is for the limited number of Fiendish puzzles; there are only 25 out of the 100. Would give it a '5' if the whole book were all of Fiendish level.