This one reminds me of Genesis of the Daleks in that Doctor and companion(s) are actually peripheral to the story being told; you could take them out of it without much change.

Exactly! I wasn't quite sure why the Ood said they were going to sing about Doctor-Donna at the end, because I couldn't see that they'd done anything much apart from make sympathetic noises on the day that Sigma and Dr Ryder pulled off their plan. Why weren't the Ood going to sing about Dr Ryder, who lost his life in the struggle to free them?

And I always said the Ood were Pak'ma'ra, so I kept muttering "told you so" when the singing came up!