Game books are books that, in addition to being read, are played like a game. This can include books with branching plot lines, book with special game rules, activity books, mystery books, hidden picture books, and various similar genres. Most game books are designed to be solitary endeavors for a single reader. Game books date back to the 1930s and peaked in America in the early 1980s, however, they were mostly killed off by the growing video game market. However, even to this day, they are still being made.
I really liked game books as a child, and, to some extent, I still do, but I find them to have serious limitations that hinder them. I discuss each genre in detail below.
In general, I don't care much
Branching Plot Books
Branching plot books are stories where the reader is allowed to choose, from a limited number of options, how the plot will progress. Books like this include Choose Your Own Adventure and Find Your Fate. I owned several of these growing up and read about a dozen more from my school's library. These tend to be targeted toward children and young adults so the stories aren't that great, and they rarely present a coherent story line. Instead, each branch takes the reader down a path that alters the reality of the fictional world. For example, you could take one branch and pull off your teachers face to reveal a space alien, but another branch will have you embarrassingly tugging on your very human teacher's face. I prefer those stories where you can make decisions, but the world is fixed.
Books With Game Rules
These books usually feature branching plots, but also use rules more commonly found in pen-and-paper role-playing games to add elements of skill and randomness to the story. Examples include the Lone Wolf series and Fighting Fantasy. I much preferred these books to the traditional branching plot books and continued to like them well into my teens.
These include books with assorted games and activities in them like crossword puzzles, cryptograms, cutouts, and more; stuff I really loved in elementary school. Occasionally, you will find an activity book that goes well beyond the traditional games, like the Where's Waldo: Ultimate Fun Book. I've always wanted to make a very complex adult activity book.
Mystery books are those whose stories include clues that allow clever readers to figure out what really happened in the story. Examples include Two-Minute Mysteries and Encyclopedia Brown. In general, I don't care for these books because each mystery can usually only be solved if the reader knows some esoteric fact.
Hidden Picture Books
These are books with collections of drawings in which pictures are hidden in them. Popular titles include Where's Waldo, For Eagle Eyes Only, and compilations of the Hidden Picture games from Highlights magazine. I still enjoy these today when the art is complex and interesting.