Showrunner Steven Moffat has spoken out about the levels of surprise in the show, explaining his rationale behind them and why he won't be so focussed on them next year:
In an interview with SFX, he said:
"I was looking for the Capaldi moments every episode, saying 'We need a Capaldi moment, that moment where he's not Matt Smith, he's not David Tennant, where he's a dangerous, unpredictable, volatile character'."
He continued: "Because that slaps the audience awake, in a way. The longer you do a show the cosier it gets, the cosier it gets the nearer to death it gets. You really have to say to people 'Pay attention. He's far more unpredictable than that'.
"So now, having done that, and having blasted our new Doctor at them, we can go other places with him. We don't have to work at that anymore because people just accept him."He added:
"I won't be looking for the Capaldi moment next year because the whole show is a Capaldi moment."