After rewatching this morning I have more thoughts.
Dean calls Cas a child and really, that's exactly how he feels to me -- a child who's been abandoned by his parental figure and is stepping into that role, trying to be grown up and do the things he wished the grown ups had done, and eventually having the whole house of cards come tumbling down because he's not really a grown up no matter how much he wants to be. I mean, yeah, in the real world that kind of thing involves a whole lot less smiting and being possessed by Leviathans, but emotionally it reads like that to me.
And I love that. I just hope that I'm right and that be the end of the season, he'll be instrumental in fixing his mistakes and taking down the Leviathans from within.
Also, I love that it's Sam that doesn't give up on Castiel -- believes that despite all evidence to the contrary there's still some Cas in there. For all that Sam's had his own brushes with bad decisions and going dark side, he's consistently been the one when all hope looks lost that hasn't lost hope, especially when that hope is being placed in family. We saw it in Point of No Return with Dean when everyone else, including Dean himself had given up on him, and we see it here with Cas. That says something lovely about Sam's heart and how sometimes being that stubborn can be a good thing.
Like I said, I was a little nervous going into last night's ep, but I am really looking forward to seeing what they do with this season now, confidence fully restored that this is still very much My Show. *draws hearts around it all*