I have two reactions from the story I wish to impart:

The gas mask zombies = very creepy. Superb horror.

Jack Harkness is like a cross between Glitz and Lord Flashheart from Blackadder. That's a scary thought right there. I got the impression that his lot didn't exist before the Time Lords were destroyed, and the "time agents" are basically filling the void left by the Time Lords' untimely erasure.