2. Midnight
I love Midnight for so many reasons. I appreciate the fact that it's written and performed more as a play than a traditional episode. For the most part, all the action takes place in one room with one established set of characters, so there's a sense of claustrophobia that pervades the episode. I love that at the end of the day, we never get to see the monster. Do we really need to? The people in the room have proven that humanity is as much of a villain as anything else, with their sudden reversion to mob mentality at the first sign of crisis and their willingness to kill an innocent man. But the thing I love most about this episode is that we get the chance to see the Doctor at his most vulnerable. The creature in Midnight attacks by repeating everything you say, then by saying things in unison, until you're finally stuck repeating what it says. This might seem like kind of a lame superpower, but we have to remember that this is the Doctor. He isn't an action hero, he's an intellectual, a negotiator. In a very real sense, all he has are his words. And to see him stripped of his ability to speak, powerless to do anything but parrot words, is terrifying for both him and the audience. Brilliant, brilliant episode, and proof that the budget-saving episodes can be just as good (if not better) than the big, expensive ones.