I loved it also. Brilliantly interconnective with the rest of the series, and really sold home the legitimacy not only of Milioti's character but the gradual unfolding of her presence in the show and this season in particular. I defy anyone to watch that episode and not shed at least one tear.
I'm sad the show is ending and only has eight more episodes to go... but at this rate, I think we're in for a really great ride.
And while I agree - I think the big twist will be that the Mother is dead by the time Old Ted narrates the story, I really hope it won't be the ending button on the show.