Meh. I guess this one was just so much old-school that I haven't the slightest idea what it was about. I even watched it twice.
I don't know who Alpha Centauri is, and thus thought to myself, "Why would they call themselves that, when that's what we call it?"
The Doctor didn't DO anything. I'm rather partial to the Matt Smith thing where the Doctor stands there in front of a passel of aliens and tells them Earth is protected and they'd better not even think about it, or any of the recent Doctors play Macgyver and build an alien-whipping machine out of chewing gum and baling wire and stuff happens. Here, he talked to them, they ignored him, and eventually they conscripted the Brits and ... what? I don't even know. Stayed on Mars where they couldn't possibly survive, but working together? Waited to be picked up by ... whatever that was that I don't even understand? I'm lost. And the Doctor didn't DO anything. And neither did Bill.
I can see that there's obviously a lot going on behind the scenes, because we have no idea why the TARDIS took off with Nardole, nor what Missy was up to before they showed up on Mars, nor what that was all about at the end. But, unlike the Matt Smith era, I'm beginning to lose faith that they'll ever actually tell us.