This two-episode story is one of the tightest, best-written, and best-acted I've seen so far. It's just packed with brilliant themes and lots of heartbreak. I could write about the love story, the christological themes, the historicist look at the first world war, or so many other topics. I could rave about how these two episodes are a showcase for Tennant's consummate acting skill. I could approach them psychoanalytically, through the Doctor's dreams.
But instead, I want to talk about Meta-Narrative and about The Causes of Creepiness.
OK, meta-narrative is not the right word for what I'm going to discuss. A meta-narrative is a big story that explains everything: science, religion, etc.
What I'm thinking of is more like a sub-narrative: The Journal of Impossible Things. This is the diary John Smith keeps of his dreams, which are dreams of the truth. There are many, many layers here: there is reality, which is his past as the Doctor. There are revelatory dreams, in which he dreams the truth but thinks it's fiction. There is the Journal itself, in which he writes truth as if it is fiction. The Journal is a beautiful artifact, and a beautiful plot device. With images and text, it takes reality and pushes it into a fantasy realm (from the Doctor's point of view), while simultaneously giving that disbelieved reality a new plausibility (to Joan Redfern's point of view).
Then there is the real-fiction of his life as John Smith, which is a real life on earth in a certain place, at a certain time, with real relationships with other people, but which is less real (in one sense) than his true identity as The Doctor and more real (in another sense) as a human existence. It is a real life, for a few months, in which he falls in love with a woman in as serious a manner as man has ever done. For her, this is all the reality: love and heartbreak.
Then there is Martha, again filling in for the viewer, watching him with all of her inside and outside knowledge: only she knows all the stories.
The second theme I want to pick up on is that of The Causes of Creepiness. The writers of Doctor Who do a brilliant job creating explanations for creepy things. What creeps you out for no reason? Spiral staircases? Gauzy window curtains moving in a evening breeze? Or maybe angel statues, mirrors, or scarecrows? Whatever it is, eventually an episode of Doctor Who will explain to you why those things are creepy—and will creep you out permanently while doing so.