Overall not as good as Mercy, about on par with Chibnall's previous effort of a fortnight ago. He hits the emotional stuff with reasonable faculty -- the final scene in the kitchen where Rory's dad sums up why they should keep going is undeniably a knockout, and the return of Kate (Lethbridge-Stewart) from 90s fanon was gorgeously done, and the bit about Amy being so important because she was the first face Eleven ever saw, too -- but the other stuff really not so much.
Rather than the arsepull of a cause we were given -- yet more fucking Time Lord nursery stories made to go away with the wave of the trusty sonic -- I think it would have been far more satisfying if it had all been a plan cooked up by the Doctor at some point in his future -- or hell, even the TARDIS knowing what the guture holds -- to help him say goodbye.
The story contains the trope I think typifies so much of what is wrong with the narrative choices of the new series. Chibnall kills off roughly a 3rd of the global population -- something that anywhere else would by seen as utterly apocalyptic -- and...
...it just doesn't matter.
At the very moment Kate gives us that number, that astronomical deathtoll that should be leading to unmitigated chaos in the streets as cars crash and planes fall out of the sky, you know that there's going to be a big sonic-green reset button being hit in the next few minutes. Oh look, 2 point whatever billion hearts all instantly and effortlessly jumpstarted as people walk away looking only mildly perplexed.
The series keeps threatening moden Earth on a scale and with events that should leave it forever changed. Verified alien contact and invasion and attempted genocide how many times now, taking place out in the open on a global scale, and always explained away or magically undone. It's all just meaningless hyperbole that throws me out of my willing suspension of disbelief and more importantly any sense of emotional connection it's trying to generate.
When you get down to it, there was only 1 person under any genuine threat: Rory's dad. With the Ponds due to leave the Doctor's life next week he's going to be put on a bus anyway, but that bus could always get blown up. I'm really glad the hammer didn't fall, but as it seems most likely he was introduced in DoaS precisely so he could be imperiled in this ep, I don't think there was any need for the pointless 2 billion.