I liked this one too. It made a proper attempt to be a story that made sense, unlike Knock Knock which didn't seem to care what was happening onscreen from one moment or the next or why. Capaldi is consistently excellent at the moment and for once they aren't overegging the arc plot- a few series ago we'd have had three mysterious prophecies about the end of the universe by now, and instead we have a big shiny door that gets argued over a lot which is much more satisfying.