As previously mentioned, there has been a bit of padding in the previous five episodes. A five-episode long journey through Cathay with Marco Polo may, in fact, have had a wee bit of extra kidnapping and banditry and so forth; however, that slow simmer of sub-plots now means we've got two whole episodes that are almost totally payoff. "Mighty Kublai Khan" brings (unsurprisingly) the Khan himself, and he's exactly what you don't expect him to be--far from a terrifying warlord, he's a slightly doddery old man with gout who lives in fear of his domineering wife and indulges in a quiet bit of gambling when she's not around. The scenes between him and Hartnell are adorable, and they're only going to get better.
Meanwhile, Ian and Ping-Cho wind up paired off in their own sub-plot, tracking down Tegana's theft of the TARDIS. This is where the amount of character development we've gotten over the last five episodes really pays off; Ping-Cho is far more detailed and realized than any incidental character in the new series possibly could be. We care about the resolution to her story, which makes it feel more grounded and realistic that the regular cast does as well. When they stand up to Marco, not knowing that Tegana has been playing Iago once again to undermine them, it feels like an earned character beat and not merely a further plot twist. It gives Tegana another chance to go swanning off and be evil, but by this point that feels earned as well. Sure, it's obvious to us that Tegana is evil, but he does a great job of getting his licks in early and often.
Nonetheless, even the longest-simmering plotline has to come to a boil eventually, and Kuiju's admission that Tegana hired him finally makes his villainy overt. Which leaves us exactly one episode to resolve Ping-Cho's wedding, Tegana's betrayal, Marco's moral dilemma, and oh by the way to get the Doctor and company back to the TARDIS. Too much to handle? No, the pacing finally feels like it's moving at just the right clip.