I really enjoyed this episode - to a point. It was the first time in a long time that I've gotten completely engaged in an adventure and just sat back and enjoyed the puzzle-solving and the spidery creep factor. Then it got preachy about landfills and toxicity and corporate responsibility, and bogged down with long explanations about biology and bioengineering. Luckily, that part wasn't long and the episode returned to the problem and the resolution... and then it just ended.
That's what has really left the bad taste in my mouth. Robertson shoots the queen spider, the Doctor gets upset, and then nothing. No closure: no repercussions for Robertson, either on the personal or corporate level, no idea of what they planned to do with the roomful of spiders. I don't subscribe to Series 9's (well, specifically Ashildr's) complaint that the Doctor never cleans up after an adventure (sorry, but I don't think it's the Doctor's responsibility to make sure that everyone and everything involved is taken care of), but this just wasn't a satisfactory end to the story, narrative-wise. It felt abrupt, like they realized they had run out of air time and had to cut the ending to stuff the final scenes in.
I did like the final scenes. I like that each of the companions have different reasons for wanting to stay with the Doctor, and that she wanted them to stay without asking them to do so. And I really like that she told them, for once, that it would be dangerous and she couldn't guarantee they would come home. I was rather surprised that in the scene where Ryan talked about his father, the urgency of the situation precluded Ryan from admitting that he felt that Graham was more family than his father was. Don't get me wrong: this was cool. For once, two characters discussing personal matters in a dire situation actually got interrupted by the threat! The spider wasn't moving at the speed of plot!
Robertson felt more like a caricature than a character, and a poorly-drawn one at that. He just didn't make much sense. I'm wondering if he, like the time traveler villain in "Rosa", is going to reappear later to flesh him out.
After the episode was over, my husband made a comment that I found very interesting. We were discussing the long stretches of spider biology that had bogged down the story, and he observed that the technobabble this season has been a lot more real-world science, rather than the unreal tech that we're used to. Because it's real-world, it has to actually make sense and explain things clearly, and thus the delivery becomes very academic and slows everything down. He then compared it to the long expositions on history in "Rosa", in which the characters had to explain to the audience who Rosa Parks was and what she did, and said that perhaps DW is trying to be more educational, in both history and science, as it once was back in the 60s.
I think the bottom line is that this was a fine episode, and so far the series has pleased me. It still doesn't grab me the way the classic show or the RTD era did, but I look forward to Sunday nights now.