This one is a particular favourite:
9. A postwar survivor's story: When Russell T. Davies brought the show back in 2005 — and yes, we're just going to skip the TV movie — he was clever enough to create a whole new backstory. Not by rewriting the show's history, but by adding a new layer. All of a sudden, the Doctor was the last survivor of a terrible war that had wiped out his entire race. The Doctor suffered from survivor's guilt and PTSD, until a young Earth woman helped him to begin rediscovering his connection with humanity. And even though this theme was downplayed somewhat in Davies' later seasons, it still informed the Doctor's relationships and gave him a greater emotional fragility, culminating in a story where the Doctor is willing to give his own life to keep the war from starting all over again. It was probably inevitable that a resurrected Doctor Who would be more character-oriented and arc-driven than the original series, but Davies managed to reinvent the show's mythos in a way that opened up a lot of scope for new drama.