I don't usually do this, but I keep forgetting my train of thought on this, so I'm going to write it down.
I liked the episode, as far as it went. But. I think it's HIGH-larious (in a vaguely irritating way) that after all the caterwauling that fangirls have done about how they don't want a woman on the show tearing Sam and Dean apart, and the numerous incidences of swooning in response to the newest male character, it's Castiel who gets Sam and Dean apart more than anyone on the show has EVER been able to do. Wow. Not one word spoken between the two for a whole episode.
Second. OK, I'm not saying it bothers me because it doesn't fit with my understanding of God. But ... Supernatural's version of God isn't all knowing? Seems like that's a pretty important part of any supreme-being-sort-of god's job description. Um, and how come God and the Yellow-Eyed Demon can't tell the future, but Sam and Ava can? And one more thing: how come Castiel can bend time to the past, but not the future? Does that make sense at all if "time is fluid?"
For all that, I liked the back story kind of a lot. And I LOVED Mitch Pileggi as grandpa. And I think there is still at least one route the show could take from here that would keep me satisfied plotwise, so hope springs eternal. (Although the "Next Week on Supernatural"s didn't give it much to feed on.) But it's not a route for the lazy, so we'll see if the show takes it or not.