Peter bloody Capaldi, with his red-rimmed eyes throughout.

Gods, yes. His death scene was absolutely masterful. And it's for the sake of scenes like that that I really don't mind about the slightly unrealistically quick'n'easy resolution to the actual Alien Threat. If more time had been spent working out detailed and clever resolutions to that, it would have left less time for all the wonderful character development and, as you say, proper dramatic tragedy that we actually got. And I'm all for the tragedy.