The Doctor visits a certain point in the future, where humanity is kept under control, in the confined space of a satellite, by a very well-oiled media-and-surveillance machine. They live their lives dreaming of being noticed and promoted by the administration, only to find out, if and when they make it to the highest echelons, that they were only brought up to be fodder for some bloated, foreign monstrosity. Drained of their life, they are nonetheless kept working and serving the system, monitoring and directing what remains of humanity, keeping them where they want them with cautious use of mass media. Keeping the thing alive requires dumping its heat on everyone else, to keep it cool and functional; this makes most of the satellite a very hot and uncomfortable place. People are encouraged to fundamentally modify their bodies and identities, the better to serve the system; these modifications can be turned against them and used to extract information from them. The Doctor scoffs at the people who don't think for themselves, and encourages them to ask the right questions, seek the truth, and grasp their own fates; to exercise autonomy and attain and enjoy freedom.
Okay. The social satire is laid incredibly thick. Yet one can't help but find it a bit underwhelming, in that it relies on allegory and grotesque fantasy to represent very tangible challenges that affect us in Present Day Present Time. I suppose it's right in the line of They Live! or Deus Ex: Human Revolution, among many, many other works, that address the concern that there is some conspiracy behind the media world we live in, shaping our lives from behind the scenes without us knowing exactly why and how. This concern is hardly invalid, but being so heavy-handed in its treatment makes one want to suggest that they Don't Shoot the Message.
That said, a very nice touch was showing that the conspiracy was hardly as competent or all-knowing as they are thought to be or as they themselves like to think they are. The Editor says that he can detect any doubt in any individual and crush it, yet he has an entire underground movement of resistance to worry about. The monstrosity is impotent without its aides and supply systems, and, much like an Upper-Class Twit, is limited to reactively shouting unhelpful orders, without ever showing a hint of a sense of leadership or initiative.
Another amusing Aesop is that, while Tyler's boyfriend's subplot is presented as fairly sympathetic and something a human of average morality would do, the narrative switches attitudes midway, presenting us with the clear message that attempting to game the system without proper understanding will only lead to the system gaming you (in contrast, the Journalist's manipulation, being thoughtful and purpuseful, achieves quite a lot).
But here's the part that makes me uncomfortable, and that appears also in the preview for the next episode; the idea that it is wrong to change the timeline with knowledge from other eras. The Doctor changes history all the time; if not for his interventions, things would go in drastically different ways throughout history. Heck, often his interventions in the past briefly threaten to change the present in stark ways. The only thing distinguishing Rose and her boyfriends' efforts from the Doctor's appears to be self-interest (greed, wanting to preserve the life of a loved one); this sounds like a Broken Aesop among the lines of Personal Gain Hurts, especially given that there doesn't seem to be a purpose to the Doctor's spacetime wandering, other than curiosity and thrills.