Don't Interrupt Gameplay
Television writers live in fear of the commercial break. That's when a viewer is most likely to flip channels and see what's playing on a competitive network.
Many games have breaks in them. It's almost inevitable in games with sequential missions. Often it's because new assets need to load.
If at all possible, create the illusion of the game being ongoing, with no interruption. For instance, in Grand Theft Auto III, an area of blue light indicates where you need to go to receive your next mission. This device accomplishes many things simultaneously. When you play the game:
Empire, Morrowind, and The Sims are examples of other types of games that keep the flow going. Online games like Everquest fall into this category as well.
Game designers will continue to pioneer ways to create the feeling of continuous game-flow.
Another way to say, "Don't interrupt the game" is to say, "Always give the player something to do."