If I can borrow some inspiration from you readers again, let me say that whoever made the connection between this pair of episodes and Audrey Niffenegger's lovely, sad novel The Time Traveler's Wife nailed it. I hadn't thought of them in those terms but they're simpatico in theme beyond the obvious time-traveling connection. Beneath the science fiction trappings of both lies a feeling that a lot of people share: It's not easy to love someone who wanders.
That's true even if those wanderers mean well. The best bits of this episode, even if they sometimes slow the pacing particularly toward the end, drill down to the emotional core of the Doctor. His scenes with Alex Kingston's River Song after he begins to piece together that not only is this strange woman legit, she might be destined to be a companion in the sense that none of his previous sidekicks has been, are beautifully played, all the more so when he recognizes that this might be the last time he sees her. Even if it's also, in another sense, the first. Even the Doctor seems to have a hard time wrapping his head around that chronological conundrum.
There's another literary model for this that did occur to me while watching this. Watching Donna try to puzzle her way to the base reality of the world into which she's been dropped suggested that Steven Moffatt has read his Philip K. Dick well, particularly Ubik. Donna keeps her head better than most of Dick's characters, but the search for the truth comes at a terrible cost. In this patched together version of the 21st century presided over by the benevolent, all-knowing Dr. Moon, she's found happiness she never found in the real version.
Or, for that matter, in space. Is it sweet, or unintentionally retrograde, that a character defined by her starbound wanderlust would drop so easily into a fantasy of settling down and living a traditional existence? And, while we're speculating and we all (presumably) know the big twist at the heart of these episodes, why would the computer make everyone live in a 21st century London?