If all you've read is The Doomsday Book, you know what I mean about emotional swings. To Say Nothing of the Dog is mostly silly and funny, despite the topic. Blackout/All Clear is back to The Doomsday Book level of things. There's also a short story she wrote before the rest of it called Fire Watch, which fills in a little info.

I am the Doctor, and THIS... is my SPOON!