I think the episode cheated quite a lot with the landlord character, hinting that his abrupt appearances and disappearances were due to an inhuman nature, in order to make it a surprise in the end that he is in fact human.
The Doctor’s chummy relationship with the crazy, genocidal Master/Mistress makes him a much less likeable hero to me, but Moffat has talked about how much he likes the friendship angle between the two, so I’m not looking forward to seeing what/who’s in the vault. It’s too bad that less hammy characters like David Suchet’s are inevitably one-offs.
More than any other companion, Bill reminds me of Ace, a character who was consciously crafted to represent a character who captures the youthful spirit of the times. I didn’t care for Nardole in his original two appearances, but he’s grown on me, and he should have been in this episode more.