“This is a kindness.”
Science Fiction Television shows always have that one episode, Star Trek had Yesterdays Enterprise, the Mirror Universe(s) episodes, Stargate(s) had them, that one episode where an alt.reality version of the main character meets the main cast and for the rest of the show you either hate it or enjoy it.
The Girl Who Waited was enjoyable because it comes back to the main thing with the Doctor’s Companions: What happens once he leaves them? Or, they leave him. And, so on. While School Reunion brought the Doctor and Sarah Jane together, this time Rory fails to save Amy in time.