7. Partners in Crime
This is an episode about tiny little aliens that are made out of adipose. That's right: fat monsters. Who vetted this script, again? Sure, there's a cute bit of slapsticky goodness at the very beginning, when the Doctor and Donna are both investigating the same thing at the same time without knowing it, but that's really all this story has going for it. The script is feather light and has little to no substance to it. I'm not saying that Doctor Who needs to be doom and gloom all the time or anything like that. Far from it. But for a show that is capable of telling literally any type of story you can imagine, it feels like a crime to have a story that has so little going on in it.