What has made the series such a hit?
The quality of the past few years of programming definitely contributed greatly to the slow growth of a large audience. Capturing a large U.S. audience definitely required patience. Doctor Who previously aired on PBS during its U.S.A. heyday in the 1970’s and 1980’s. The audience, while very enthusiastic, was also rather small. When the return of the series debuted on the BBC, there was already a large audience that, like Susan McGalla, was familiar with the iconic time traveler. In the U.S.A., a larger audience had to be built from the ground up. The previous Doctors created the foundation for Capaldi and the new time-lord has really done well.
One reason this may be so is Capaldi’s age. We are getting an “older” Doctor once again and this is a good thing. There’s nothing wrong with the youth the previous three Doctors presented, but an older version of the Doctor is more believable. Sure, time-lords regenerate and that means they can take on young appearances even when they are several hundreds of years old. That is all well and good, but it is more believable when a person speaking with the conviction of age and experience looks the part.