I might be alone in this regard but the Lisa-Ben story in season 6 is my favorite aspect of the season. It is Dean at his most different and uncomfortable, i.e. interesting. Overall, I think this storyline is worth telling. There is just something to seeing Dean trying to be a father and partner. (The writers clearly picked up on this given that they expand upon the father idea with Jack) But I don't like the ending of this story. The finality of the resolution is exceptionally harsh and while Ackles sells it well enough it feels like a regression of Dean's character. Moreover, this episode has a vibe of just going through the motions to wrap up a storyline that writers OR fans lost interest in. It is the big disappointment in the season.