The Empty Child/The Doctor Dances has a lot of things that should appeal to a lot of different people. Aside from being an all-around splendid story with a strong, sympathetic female lead, it has a fantastic World War II backdrop that will charm both history buffs and fans of BBC period dramas. There's also the whole matter of the gas mask monsters, which for a family show are actually a fairly gruesome bit of body horror. That shouldn't hurt your case with horror movie fans. The fact of the matter is, this story is tremendously popular because it ticks all the boxes for most people. Why should non-fans be any different?