I'm a week behind, so I just managed to watch this episode, but I have to say that I absolutely loved it. My only real complaint is that I was expecting the dinosaur to be more important. Nope, crazy clock robot sets it on fire.
One thing that I both like and dislike about the Doctor is his memory. "The Girl in the Fireplace" is a heartbreaking story. And here, while the Doctor has a vague sense of familiarity with everything going on, he doesn't remember Reinette. It makes sense given how old he is that he wouldn't remember one random girl from a thousand years ago, but from an audience perspective, it seems kind of cold.
I think Clara was my favorite thing about this episode, which is strange, because I've been pretty ambivalent towards her so far. The Companion exists in this show as a way for us to relate. We're not the Doctor; we are the Companions traveling with him.
Rose saw the Doctor change, and she hated it at first. Tennant slept his whole episode away, and Rose felt abandoned. However, once she finally saw him in action, she grew to accept that he was still the same old Doctor.
Clara sees Capaldi in action right from the start, and she doesn't like it. He's old. He sounds different. He acts different. He barely recognizes her. And she is understandably freaking out. I absolutely loved the scene with her and Vastra where she loses her temper.
Now...who is Missy? The way that Moffat writes his show, I naturally assume that all mysterious women are River Song

Tasha Lem was almost definitely originally conceived as River (whether Moffat says so or not).
Is Missy the girl in the shop (I always wanted this to be Rose)? Is Missy a new version of River? Is Missy a female version of The Master (The Promised Land sounds an awful lot like Utopia to me)? OR...is Missy just a brand new character with no connection to any old ones? That would be weird.
My prediction for the final episode of the season: Missy has collected all the bad guys that the Doctor has faced throughout the season, starting with Robot Man, and then there is some big ultimate battle where the Doctor faces them again. The Pandorica...the Wedding of River Song...the Time of the Doctor...Moffat loves bringing all the bad guys back in the same place!