That was probably the best episode of the series thus far. For the first time this year we had an alien species that was actually interesting. It's such a lovely idea to have a species who travel the stars lamenting the unmourned dead, and such an ideal fit for today's events in the real world. Not sure if that was deliberately timed, but it worked beautifully regardless.
It was another Hartnell-esque historical for much of the run time. The Sci-Fi elements were fairly light, the plot favouring the drama of the situation more than the alien visitors. Once again, as in 'Rosa', I learned a fair amount about a historical period I previously knew very little about, so, yes, very Hartnell-esque again.
I don't think it's a coincidence that the best episode of the series so far also happens to be the first one not to be written by Chris Chibnall. That remains something of a worry.