While I loved the twist regarding the "monster", and got a huge kick out of the old-timey flashback with the Doctor and Clara, I have to admit the rest of the episode just... didn't really do much for me (at least on a first viewing).
The story just felt overly-familiar-- it's yet another community where "all is not as it seems", where there's yet another mad, alien-controlled leader, and where once again people are mysteriously disappearing and/or being experimented on.
And while the Vastra/Jenny/Strax combo was fun to see once
, I'm not sure they're really interesting enough to keep revisiting. There's only so many times you can keep hitting the same notes with those characters.