Season finales can be a tricky thing, especially when there’s no prevailing indication that the series will be renewed. The writers need to bring the season arc to a relative close while preparing for the possibility of a season to follow. In this case, the challenge may have been more than the writers and producers were capable of handling.
Actually, the first three acts of the episode were a logical extension of the previous episode. As obvious as it was, I never picked up on the idea that Meg was actually a human being possessed by a demon. Just that little piece of information is enough to make sense of some of the season arc elements. It also points to the most obvious direction for a final confrontation.
Like the previous episode, Meg wasn’t nearly as annoying as she’s been in the past. The exorcism scene was a nice touch, because it allowed Dean to show the darker side of his personality. Dean is right to be concerned about his lack of remorse for causing the deaths of human beings. He was already seeing himself above and beyond normal human society, and this would be a big step towards becoming the very thing he hunts.