The gaming industry is huge, and it can keep its audience consumed for hours, days and even weeks. Some play the same game over and over again—and occasionally, they even get out their 15-year-old Nintendo 64 to play some Zelda.
Now, I am not a game designer. I actually don't even play games that often. I am, though, very interested in finding out why a game can keep people occupied for a long period of time, often without their even noticing that they've been sitting in front of the screen for hours. I want my apps and products to affect my visitors in the same way.