This was a really good episode. Though I liked Ruby well enough last year, I was mostly ambivalent about her returning, not anything against the character, I just felt her story was done and there wasn't any need to revisit her. That said, having her as the central character in a Doctor Lite episode was the perfect way of bringing her back without "tainting" the ending of her arc last year, and it was good fun to see her mother and grandmother back.
A common complaint everyone makes over the year about modern Doctor Who is the fact that everyone always acts so shocked when they learn of the existence of aliens, despite there having been several extremely public alien invasions and other incidents involving aliens happening on the show. This episode provides an explanation to that with their being fringe elements in society who actively disbelieve this as lies being perpetrated by UNIT and the government, which sadly in light of recent real world history might be one of the most believable things to be depicted in this show. Indeed, in some ways this episode is commentary on how Twitter "truthers" are permeating our society. And while the Doctor's sermon to Conrad at the end did border on being a bit too preachy, I'll accept this is the kind of situation where the subtle approach would have made it a bit too easy to dismiss. As it is, I'm sure there are many who will still miss the point.
Not that I want to be "That Guy" but Conrad turning out to be a piece of shit was obvious before the episode even aired. As soon as I found out Ruby would have a love interest and that love interest would be a white male, (half jokingly) commenting "Ruby's with a white man? He's obviously up to no good. We can't have decent white men in today's woke world." And what do you know, that turned out to be true. For the record, I'm not bothered by the show (or any others) "vilifying" white men, I'm just pointing out an obvious and predictable trope.
Badass Kate was certainly a highlight to this episode. And while I was pretty certain Conrad wasn't actually going to be killed (Doctor Who is aimed at a child audience after all) that scene did leave me guessing all the same.
One minor quibble, I thought Conrad's friends cosplaying as the alien monsters looked scarier than the actual alien monsters did. Mostly the cosplay monsters looked "real" while the actual monster was obvious CG. But meh.