The subtitle of this book is: "How Today's Popular Culture Is Actually Making Us Smarter." The idea is that current movies, TV shows, and video games are becoming more challenging, demanding more mental activity from the consumer, than in the past. And, hence, make us smarter.
Fair enough. Johnson's thesis is of decent size for a longish essay in (say) Wired. But arguing for it in a book makes for a lot of repetition. There is no point so obvious that Johnson will let go without mentioning. There is no element in his argument that he doesn't beat to death by saying it over and over again. And I think his argument is weakened by not considering some pretty obvious objections. (For example: "Is current popular music making us smarter? Hah!")
Or to quote an unimpressed Amazon reviewer:
Let's assume pop-culture is making us smarter. A different question would be, is it also making is better? Is it actually good for us? Is it building character, courage, heroism, altruism, and charity? I remain unconvined that it is.