The End of the World
And in episode 2, we get diverse aliens, Britney Spears, Rose befriending a local, being under threat, a swift resolution, the first mentions of the Time War, and a scene about chips.
Almost as important to get episode 2 right as episode 1, and this does pretty damn well.
Tooth and Claw
However, by series 2, things are very different. The Doctor's established. Rose is established. So we have Scotland, a werewolf, martial arts monks that not only exist for no reason, also vanish for no reason, and the beginnings of Rose being smug in time and space. Impressive werewolf, though.
The Shakespeare Code
Perhaps the role of episode 2 is to set up the strengths of the companion, to really bed them in. It didn't really happen in TEotW, as Rose was damsel in distress with Jabe as assistant. Here we've got Martha's feelings for the Doctor in the mix, some witches, some glib cultural references. It's fun. But not on a par with
The Fires of Pompeii
which is possibly the beginning of the end for Tennant's Doctor. Lots of angst about not being able to change history, you see. Reminding us that Donna will challenge him, will ultimately be more human than he is. And sometimes she'll be right.
The Beast Below
We're still establishing a new Doctor and a new companion. He doesn't interfere unless there's a child crying. Amy gets separated, gets nosy because she's a nosy person, and we get the beginnings of mystery about her crack
Ranking for Episode 2
Series 4 - Series 5 - Series 1 - Series 3 - Series 2