1. Dalek
"Why don't you just die?!"
Dalek is one of the classic episodes of nu-Who. Because in the run-up to this episode, it was not clearly known if the Terry Nation estate would allow for the Daleks to return or not. This was to the extent that the producers actually prepared to replace the single Dalek in the story with a new alien. But that significance isn't the reason why this is number one in our list today. It is because of Eccleston's performance. For the first time in nu-Who, the Doctor was the merciless fury that he needed to be in order to end the Time War. The episode allows a direct comparison between the Doctor and the surviving Dalek as he ends up in a similar predicament as his foe. At the end of the episode, it is only van Statten who stops the Doctor from killing the Dalek, and subsequently he has to deal with what he has become. Eccleston brought some real maturity to those scenes, and I'm not sure if any of his predecessors could have performed in such a believable way. I believe that it was this episode that secured the future of new Who. It wasn't afraid to link to the past with the first new appearance of the Daleks, but more importantly it was able to show a situation that many people could relate to the length that some people will go to seek vengeance. Eccleston went dark here, darker than any previous Who episode and it was a good direction to take as it resulted in real depth being shown and prevented the series from being labelled as a kid's show. It was Eccleston's performance in Dalek that showed that this was no longer the semi-kooky eras of Colin Baker and Sylvester McCoy anymore and deserved to be taken seriously. So that's what I think. What do you think? Feel free to comment!