I found this episode slightly weaker than the brilliant Under the Lake, but it was still a very satisfying two-parter, all in all. I liked the timey-wimey-ness of it all and the setting of the Russian village in Scotland was great, but I found the ghosts to be a lot more interesting than the Fisher King and while I understand why it was done, it was kind of a shame that they were sidelined a little two make more time for their boss, who was neither all that interesting (standard Who-fare villain, really, as far as motivations and the evil, sonorous voice go) nor as brilliantly creepy as the ghosts were.
In terms of the characters, the Doctor and Clara were pretty good, but the other characters didn't really feel all that much more fleshed out than in the previous episode, but that wasn't all that character-driven either, so I didn't expect this one to be. Bennett was the one exception, and his portrayal was ace. I could have done the without the love story, especially between Lunn and Cass (Bennett and O'Donnell was okay imo), but it was such a small part of the story that it didn't really hinder my enjoyment either.
Also superbly directed, which is something that I don't really notice unless it's really good or really bad, so that's a compliment.