You've got to feel a little sorry for Matthew Graham. He got lumbered with the “can you do us a replacement script in 5 minutes and no budget” story in season 2, which to this day is unfairly underrated (seriously check the DWM poll of polls), especially since it had the awesome scribble monster.
He finally gets another crack at it, a two parter no less, only he has to follow the Gaiman episode and, if that wasn't hard enough, the masterpiece that was Season 3 of Ashes to Ashes. He was never going to come out of this one with anything other than faint praise unless he delivered an out and all-time classic.
There is to compound the problem the fact that the story was immediately overshadowed by the Cliffhanger to A Good Man Goes to War. There is though much to enjoy in the run-up to that Cliffhanger. This is reminiscent of the two part “The Impossible Planet”/”The Satan Pit” in that it is a rare example of New Who plundering the tropes of Old Who. Specifically this is a structured very mush as a “base under siege” and “rebels v colonist” type of story that permeated the show from the Troughton to Baker years. There's also more than a hint of the Cartmel era in the “right-on politics” and manipulative Doctor. This is a double edged sword because as enjoyable as these kisses to the past are, they also make the story feel highly derivative particularly in comparison to the stories that precede and follow it.
It is to Graham's credit that he doesn't play to any great degree on “who is the good one” and to the extent that he does its in respect of the Doctor, with the answer being “both”. My favourite aspect of the episode is the relationship between Jennifer and Rory. Jennifer story is ultimately sacrificed for a cheap “monster” finish, but I liked the steady build in her resentment to the humans. Rory is shown once again to be highly compassionate and thoughtful and doesn't Amy resent it! The writing for Amy and Rory has been much better this seasons. They feel much more fully formed and consistent and more of a couple. Amy's characterisation is almost a throwback to last season in this story, but now it feels like we are seeing an aspect of her personality rather than the ONLY aspect of her personality.
I could have done without the “hey isn't your dad great” subplot. Unfortunately it became running trope of this season to the point where its now clear that the Moff really wants his kids to know how much he loves them. There's nothing wrong with that of course except it became far too repetitive. We now have “the parent agenda!”.
All of which brings us to Amy's pregnancy and the finale/Cliffhanger. Now before I go any further there is the issue of the Doctor killing Amy's ganger. Not surprisingly this caused some consternation with plenty of people saying that it wasn't necessary. It actually was. The Ganger was ultimately an unwitting spy and would have died as soon as the Doctor rescued Amy anyway. On top of that there was no guarantee that Kovorian and the silence would have kept the original Amy (and therefore the Ganger) alive once Amy gave birth.
What is clear is the Doctor obviously had all of this in mind prior to the beginning of the episode. So we basically have the Doctor reverting to the “master of chess on a thousand boards” persona of his seventh incarnation. Events are manipulated from the very beginning by the Doctor. The whole story is an excuse for the Doctor to work out what is going on with Amy and how the Ganger's work. He must know that this was a turning point for the use of Gangers (this is the exact turning point for where they are recognised as having “human rights” in Earth's history). So he is also taking the opportunity to right a wrong and teach and manipulate his companions at the same time. Somewhere Ace and Benny are saying “join the club”!
Good stuff, but better was to come.