That opening looks and sounds like an ad for a savings bank.
"For your own sake, understand this: I am the Doctor. I am coming to find you. And I will never, ever stop."
"Clara said I shouldn't take revenge. You should know I don't always listen."
"It's a killer puzzle box designed to scare me to death, and I'm trapped inside it... hah! It must be Christmas."
"I have to tell truths I've never told before. That's the only thing that stops it."
... Must have spent so much on effects that they didn't have anything left to spend on a cast...
"I'm not scared of Hell. It's just Heaven for bad people."
And now he's beating himself up. You can take the Doctor out of Glasgow, etc. ...
"I haven't time travelled. I've just been here a very, very long time."
"Personally, I think that's a hell of a bird!"
... For an episode that's basically one long monologue, this one worked remarkably well. The time loop - well, not really, but had the same narrative effect - was also rather nicely done. Apparently some people are grumpy about it. It's as if there isn't already a precedent for a solo Doctor story set in Gallifrey...