This was a good episode with some good character moments and an interesting mystery where things were not as they seemed, thanks to Michael. Maggie, the new Hunter from the other universe who was resurrected by Lucifer, went after what seemed to be a Ghoul, but turned out to be something else entirely-- she was captured and Sam and Dean went to the rescue, as did Mary and Bobby on their own.
Maggie was actually barely in it, spending most of her couple of scenes dangling from her toes. The guest character had more screen time and was of a very familiar and unpleasant type, but she got to receive some advice from Dean on how to deal with a less-than-ideal father, with the implication that there might be a reconciliation.
The Ghoul turned out to be the return of the Djinn from a few seasons ago, now super-sized thanks to Michael's plot to take over the world or reduce the world to chaos or whatever he's trying to do. There was a very interesting moment when the Djinn went into Dean's head to seize his nightmares, but recoiled in pain or terror-- was it because of everything that Dean has been through (e.g. thirty years in Hell) or because of something Michael left behind? Or because Michael is still in there?
But the main development in this episode was with Mary and Bobby. Bobby's nightmare was his dead son from the alternate universe, which he was loathe to share with Mary, and this was keeping them apart. But by the end of the episode their coupledom is official and they are off on sabbatical to a remote cabin (belonging to Sheriff Jodie or Sheriff Donna, I forget which) while Bobby recovers and they work on their relationship. I would have much preferred that Mary become a regular part of the team, like Cass or Jack, but I can live with her showing up only occasionally-- as long as they don't kill her off!