Definitely a fun outing in my eyes. I can't think of another heist film/tv story done with science fiction elements, so it felt pretty original on that count (and for the show itself as well). It seemed to follow all the heist tropes as I know them - impossible target, assembling the team of carefully chosen experts in their field for each hurdle faced, and then... time travel turns up and makes it a twisty clever loop, something Moffat's brought in spades to his era of a show (about time travel no less!) that had been mostly missing for most of it's run. Oh yes and of course a monster too! Nothing deep, but certainly fun. And again, I think the directing of the show was better than usual, so maybe this is something they're working to bake into the show now.