A good game keeps you at the edge of your ability

As you successfully lock in Tetris puzzle pieces, you get three kinds of feedback: visual—you can see row after row of pieces disappearing with a satisfying poof; quantitative—a prominently displayed score constantly ticks upward; and qualitative—you experience a steady increase in how challenging the game feels. This variety and intensity of feedback is the most important difference between digital and nondigital games. In computer and video games, the interactive loop is satisfyingly...