Season 3, basically.
I thought Dean was his happiest in a long time for much of season 8 (although now I realize they were building him up to tear him down), but many fans kept saying Dean had become a "housewife," so I wonder if fan response will ever allow Dean or Sam to not just drown in angst.
Jensen and Misha can sing, and Mark can too, but it's going to be one of those moments that is going to be seen as shark-jumping, because it's so difficult to pull off. I didn't even like the Buffy one all that much.
It's funny, because I've heard fans saying for years that they want this, yet I have a feeling they're probably going to tear it apart.
The part that interests me most is about this person who is following Dean and Crowley. I wonder if it will be a hunter.