Utterly incredible. There's fun characters, dialogue, and quotes. It's a very interesting mystery with an extremely satisfying conclusion/solution. All of the parallels between the Doctor's life, that of Baba Yaga, and that of Vasilisa are gorgeously done. I even love the subtle nod to An Unearthly Child, where the Doctor's recruited to try and make fire for members of a primitive culture. We also get a much fuller range of Jo Martin's performance as the Doctor, and she excels.