It was a pretty good episode, but not a great one. (I'd have to watch it again to be sure) I still don't understand why or how Peter got erased, just why he got brought back. Since there are still eight episodes to round out the season's story, I hope we'll find out more.
I was most impressed by the scene with Olivia and Nina at the end, where Olivia made her promise to build a relationship with her even if Olivia forgot all their time together. Flash back to the early season episode about the Alzheimer's wife and her husband; in a way, Olivia was going into a sort of Alzheimer's journey into a different reality - of course, usually it's the older character that happens to, not the younger. Of course, the Stephen Root character did it all the wrong way - trying to force a scientific solution. The proper response to shifting realities is to try and maintain relationships, to keep "the bridge" open that way.
As for the question "What happens now" with the blue and yellow realities - which is which, and which takes precedence over the other - I think the watchword is continued bridge-building. After all, in this world, the red and blue worlds have built a bridge and are working in alliance. Peter and Olivia's love is the bridge between the yellow and blueverses. Walter has not "blue-ified" yet... will he ever? I really hope so.
Loved September's line, "I have a theory..."
I get the sense some viewers won't like the answer to the question "Why did Peter not get erased" because really it is very lovey-dovey (as opposed to timey-wimey). However, the Olivia-Nina exchange did a lot to get me on board with the idea that even the yellow and blue realities could coexist, as the red and blue worlds do.
I thought some of the lines for Olivia elsewhere in the episode were weak. I only tolerated the furtive glances between her and Lincoln because this episode, after all, was "A Short Story About Love." Okay. And it would seem that
so I'm looking forward to the reaction to that action.
Still don't know WHY Peter was erased, though, and that bugs me a little because we're still waiting for the narrative to become clear. But this is the third act of the season we're heading into, so...