I was excited for this but I found it underwhelming. I don't care about Clara at all so that's an issue for me. And plot holes, geez, what was even going on here.
To me it felt like an attempt to recreate or recapture the success and the a atmosphere of episodes like Blink and the stuff with the Silence. But it just didn't work that much for me in the end.
Let's go through the plotholes because after watching it for the first time, i thought there were tons. upon second viewing, it all made a bit more sense. I will answer your questions!