Re:Not a bad story line, not a bad set, not bad horror creatures
I think the rest of your post pretty much contradicts that opening line. Well, except for maybe the horror creatures.
..since the start of the episode he is being an ass.
That pretty much sums up what has been wrong since they regenerated the Doctor. I'm not blaming Capaldi. I think he's doing the best with the scripts he's been given. Somebody just needs to remind the writers that "the hero is an ass" is not a formula for a successful show.* Especially one that is supposed to be nominally child friendly.
*You can get away with it for an episode here or there, but not constantly.