I think that most of this episode was unnecessary.
No wait, let me start with what I liked. I liked the back story on Mary and her family. Mitch Pileggi was much fun; he handled the YED character very well. I also liked the last few minutes of the ep, because it moved the story forward at warp speed (see what I did there?) compared to the rest of the ep.
But I wanted to see how things happened in the first place! We still don't know that - and now we never will. Unless this is what really happened... And if so, is Dean is going to have some new mental anguish wondering if he's actually the one that caused YED to first set his sights on Mary? Like, has he always gone back in time or did that bit of history really change and then not cause any fallout? Castiel hints at the end that Dean didn't cause the whole debacle, and I'm betting that'll be the last we speak of that.
Time travel is hard, Kripke. I'm sorry but y'all didn't pull it off well for me in this ep.
"You have to stop it." "Now you know what we know." Fuck you, Angel of The Lord. You could have shown him, told him. It wouldn't have been a whole episode, but it would have fit better. Letting Dean think he could save his family when you knew he had no chance was a dick move. I can't see it serving any purpose other than tormenting Dean. So - why? Weak writing or plot device to hammer home that Castiel is non-human? Something else? Anyone?
Also - please never say the word "endgame" again on screen, ok? You used up all your times during this ep.
I did like the last minute or so of the ep, when we finally got the intel on what Dean needed to stop and Dean went off to find Sam. I'm really, really hoping that Our Boys talk next ep. I know, that's not the way it's going to work. But I keep hoping.