(As always, no spoilers. If you came here as the result of a Google search for "Doctor Who Spoilers", shame on you. Honestly. Why not just watch and enjoy it in real time?)
All I can - and will say - about this episode is that this is probably the best resolution to a two-part episode since the "Army of Ghosts/Doomsday" Season 2 finale.
It's a difficult episode to write about without spoiling, because one of the strengths of the episode is that it takes several set-ups from last week's "Silence in the Library" and flips them around. There's one clever use of television conventions to help convince the viewer that, yes, something is going on. A character who seems set up to be the "villain" of the piece is shown to have much more noble intentions than expected. Much is said by not being said at all...but is subtly spelled out in hints, in insinuations, and in the small details that may or may not be said.
However - and this is the only way I can talk about the episode - is that, in many ways, it resembles Moffatt's Series One two-parter, "The Empty Child/The Doctor Dances" thematically, if not structurally. In many ways, the Ninth and Tenth Doctors are mirror images of each other - the Ninth severely traumatized by his past, and aggressively acting it out; the Tenth burying impenetrable levels of melancholy beneath a jovial, almost manic exterior. But one of the key themes of the "Child/Doctor" is that, despite severe trauma, life and - and will - prevail. The Ninth Doctor's joy at exclaiming "Everyone lives - just this once!" is palpable, and the viewer feels it.
With "Silence/Forest", it gets flipped and turned into "Everyone dies....but not every day." Given the huge amount of foreshadowing about choices, about knowing the future, it would be easy to postulate about where the season is heading. (Of course, we could all be wrong about it). But in this story, the Doctor faces severe trauma - the kind of trauma that was only suggested by the Ninth Doctor's history. And a fake-out ending - an ending which has played fair with the viewer - reinforces what is probably the Doctor's main raison d'etre...that deep inside, the Doctor is a man who does not want to see people die...and who fights for life at almost any cost. And the final interchange between the Doctor and Donna is probably one of the most endearingly human - and honest - interchange between a Doctor and a companion.
There have always been turning points in the Doctor's history - many of which have been seen in the classic series. In many ways, this story shows another turning point in the Doctor's history...and is, thankfully, severely and delicately underplayed.
Good move, Mr. Moffatt, good move.
The franchise will be in good hands come 2010.
(Note - Episode 12's title has not been officially released. When I get around to reviewing it, I will - in the spirit of non-spoiling - make up a title for it. And again - shame on you for seeking spoilers)