3. The Next Doctor
This one had 'gimmick' written all over it - David Tennant had recently announced his imminent departure from the role of the 10th Doctor and, as luck would have it, the story that ran hot on the heels of that announcement concerned a character that claimed to be a future incarnation of the Doctor. It's even called The Next Doctor, in case there was anyone left on Earth whose interests weren't already piqued by those factors. It was a relief then, that amidst all the hype, speculation and quest for ratings, The Next Doctor was a fantastic story - taking an inventive premise and running with it, introducing one of the most effective human villains in the show's long history and wrapping it all up in a big, snowy ball of Dickensian Christmas cheer. I'd hazard a guess that this one set the template for Moffat's Christmas episodes. David duo Morrissey and Tennant bounce off of one another beautifully in this would-be multi-Doctor story, while the twist (spoilers: he's not the Doctor after all) gives the episode an emotional second wind that is just as enjoyable to watch unfold as the previous novelty of two Time Lords. The direction is also glimmering - with the Victorian Christmas deftly realised from the outset and haunting images of Miss Hartigan - in striking red - marching callously through the snow-laden cemetery to introduce her Cyberman friends. It's gothic, it's as Christmassy as it gets and it's quintessential Doctor Who - and it also saw the first flashback of previous Doctors (something that seems to happen every other episode nowadays) in the new series. What's not to love? Perhaps the Cyberking was a bit much.