All in all, I think if they’d ended the series with this episode, I would have been satisfied (and I’m assuming if the series had ended there, they wouldn’t have Sam popping back up). It would have ended as sort of a downer, but I really don’t think the Bros. Winchester could ever have a happy ending. Not in the long run.
I’m thinking Chuck the Prophet was just a prophet. When he vanished in a puff of…sparkles, I thought “What, no fiery chariot for him? Just poof, and he’s gone?” not “Oh, so he was God all along!” Him being God sort of makes sense for this episode alone, but not really the rest of the show.
As for Sam coming back, what’s the significance of the lamppost flickering and going dark? Just something generally supernatural, or is there something specific associated with it? Because, if he’s back from the Pit that quickly, it seems sort of…dissatisfying. Though, I guess they could just be echoing the beginning of season 4.