I've watched it through twice so far (and I've been itching for a third time), and it's fantastic even on rewatching, not to mention you get to see things you missed before because you didn't know whodunit. On the second watch-through, Hardy telling Miller that she did good work on the case made me tear up.

We just watched "City of Death," which is a fantastic episode just on its own, and there's a scene in which the rich snobby guys have captured the Doctor and Romana, and are interrogating him, and he's just messing with them. It's absolutely hilarious. My favorite line from that scene: the rich guy asks, "Who sent you?" and the Doctor, with a completely confused look on his face, replies, "Who sent me what?"