As someone who watched old Doctor Who reruns growing up, I’m quite fond of the multi-episode arc that Doctor Who traditionally used to tell stories. It’s something we rarely see from modern Doctor Who, at least not to the extent that it used to be used as a story telling device. In fact, this is only the second two-part season premiere of Doctor Who since the revival.
The problem with a multi-episode story arc is that you really need to have a good payoff to the individual episodes and the story as a whole. I’m not convinced that The Magician’s Apprentice and The Witch’s Familiar two-parter really fulfilled either side of that.