To start, here's what I remembered about this story:
I remember this being really creepy. A very clever idea and some good cheeky continuity with the 50th special. However, the actual detail of the plot hasn't stuck in my mind. The ending was a very original concept, but I remember feeling distinctly deflated. Overriding memory? A lot of tension, but nothing actually happened.My gut reaction wasn't far off, I don't think, but re-watching this was more enjoyable than that makes it sound. What I'd forgotten was the interesting continuation of Clara trying to enjoy a normal life alongside travelling with the Doctor.
In short, the character drama is very enjoyable. It's fun seeing Clara freak out when presented with possible evidence that she is to have children with the man she has only just started dating. There's some entertaining exploration of ideas around how formative experiences in our childhood can great impact upon our life choices, with Danny being given the toy soldier as a child and Clara giving a child version of The Doctor the same speech the adult Doctor had given her earlier in the episode.
There's one point of continuity that doesn't really work. If the Doctor grew up on Gallifrey and that planet was destroyed across time - there's the continual suggestion that the Doctor can't visit Gallifrey in the past because it is completely gone throughout history then how can Clara visit the Doctor's childhood? Maybe there's an explanation, but none is given. Add it to the list of bizarre leaps for which this particular series of Doctor Who doesn't feel it needs to bother offering an explanation.
The monster drama is odd. It didn't feel as much like a false ending as it did on first viewing, but there's something amiss. I think it's one of those ideas that would be great in a book, but falls flat as soon as the visual medium is used to tell the story. We're supposed to believe that the mystery creature the Doctor is hunting is entirely a figment of overactive imagination. That's fine, so what is the thing we all saw under the sheet in the children's home? It was there, on screen. All the characters looked at it while it was under a sheet? The problem with visual storytelling is that once you clearly show the audience something, you can't dismiss it as the characters "seeing things" because we are all third-party witnesses. Plus, for me at least, the story makes an initial assumption about all living things having a shared nightmare - one which I have never had.
Now if it had been a nightmare about a wolf trying to eat my feet, let me tell you about my childhood dreams...