What's interesting is that someone with the very basest of information (me) can follow along the story and enjoy it without knowing 100% of the backstory. You include just enough so that I can get people's reactions to other people, but not so much that I feel like you're retelling the entire series.

(I have seen a few episodes of 9 and Rose, one of 10 and Martha, and several of Doctors 1 and 3. No Torchwood yet, although I think I've about been converted.)