I'm rather disappointed in this episode.
It's not that the producers decided to replace the opening theme and CGI sequence with a Matrix-style glitch in a 'found footage' scene. It's not the horror element.
It's not even so much that the normally competent writer Mark Gatiss churned out something rather stupid, although it does contribute to the poor quality of the episode.
It's that the producers seem to have run out of steam for the show and are no longer interested in even trying to maintain storytelling standards so as not to insult viewer intelligence.
I mean, come on: Killer sleep sand? Really? That gunk that forms in the corners of our eyes at night and dries into crusty yellow-ish grainy stuff takes on a life of its own and devours people from within?
I realize that head writer Stephen Moffat is a one-trick pony and that this episode is basically filler until we reach the season finale in three weeks, but still, he owes us better and so does Gatiss.
I'm giving this episode the 'F' it deserves.