On the one hand, it was a fine story. A bit too procedural for my DW tastes, as in, "Oh, there's artron energy here so there must be a problem, and it leads to this guy, so he must be trying to change history, and oh, look, he is! And so let's do some research and then foil each obstacle as it comes up." There were no surprises and no twists, but I'll admit those aren't necessary for a good story.
On the other hand, it lacked cohesion and believability. It tried to put time pressure on the TARDIS team to get James Blake driving the bus to pick up Rosa with a full load but showed very little of how they actually did it (how did they actually commandeer that new bus?), and what they did show (Graham and Ryan at the river, Yaz with Rosa) was leisurely. Also, in multiple scenes through the entire episode, the team discussed what they were doing in full view and earshot of others without any repercussions.
I think, though, it failed for me in two very specific ways. First, it didn't make me care about the villain at all. (Sigh. I can't remember his name.) Sure, there are people out there whose only motivations are their hatred of -fill in whatever group- but put that in a story and that makes a one-dimensional character. Why was he the way he was? And especially, why, after killing so many people (for an unknown reason, too), did he decide this was what he wanted to do? Nothing indicated that his original killings were racially-motivated, so what happened that made him go in this direction? Now that's a story I'd like to hear. (Side note: This just reminded me of the last episode of Broadchurch Series 3, where the serial rapist explained his motivations, which were dark and twisted. Not that I'm saying DW should go this route, but that scene is what stuck with me from that series.)
Second, I feel that this episode entirely wasted what should have been the focal scene of the episode: Rosa on the bus. Sure, it was a fine depiction of a historic moment, but it could have been so much more. The best bit of it, to me anyway, was Graham's refusal to stay on the bus and pretend to be a racist white person - but the Doctor told him he had to stay to keep the bus filled, and so the historic scene proceeds with everyone staring mournfully at Rosa. But imagine if they had allowed the actors to actually show the internal conflict, meaning, Graham, Yaz, and the Doctor ducking their heads and being unable to meet Rosa's eyes and hating that they have to betray her to make history stay its course. Meanwhile, Rosa is appalled that these people she thought supported her - who she saved in the first scene - won't lift a finger to help, won't even give her silent support, but she does what she has to do, and, as it happened in the episode, she gets some affirmation from Ryan and his fierce support as she's led away. This is what I'd have liked to have seen.
Of course, to make that scene make sense, there would have had to be more established in the relationship between Rosa and Ryan. I would have liked to have seen a bit of the meeting between Rosa, Dr. King, and the others, so see what it was that opened Ryan's eyes. As I think about it, this episode could have been a great source of character development for Ryan, as he gets to see these people fighting for what he takes for granted. But no, if any such development took place, it was off-screen.
I'm also quite disappointed that the episode was wrapped up in a neat bow. Why didn't the Doctor take Ryan to task for not only playing with a weapon he doesn't understand but also for sending a man randomly back in time? Why doesn't she care where the villain ended up? This smacks to me of "he's a villain so I don't care what happens to him", which is very un-Doctor-ish. The Doctor should have also addressed Graham's misgivings about staying on the bus, assuring him that she knew it was horrible for him but it was the necessary thing to do. Instead, we got an "everything's going to turn out just fine" speech, which rang hollow in our contemporary American racial climate. It's pretty telling that the Doctor's "see how good it is" event happened twenty years and three Presidential administrations ago.
I'm hoping that the villain shows up again later in the season, so that we can find out more about him and where he ended up. Then I can excuse them not addressing that here.
Husband's verdict: He did not like this episode. He was already pre-disposed to not like it because he doesn't like stories with agendas, and it was certainly preachy (though, I'd say it was as preachy as I expected it to be, but not more preachy), and so he didn't care at all. He also really disliked how much lecturing the Doctor does to the companions. This is not a new complaint of his - he noticed it last episode. However, the episode didn't make him angry, so that's good. He's still waiting for an episode to love.
Oh, one question: Do history classes in British schools really focus on Rosa Parks that much? I mean sure, my history classes in my American schools teach about the incident but not in the detail that Yaz had. Not to mention that it's a different country's history - I cannot imagine that American students would have such intimate knowledge about British history.