That was a mediocre season finale. It makes me think the show is running out of gas. I wouldn't be surprised if the next season is the last although I guess if the ratings are good and the actors are willing it will go on and on.
What I think they need to do is scale back and get away from the story arc that is the end of the world every season. I'm really tired of all the angel stuff. Just let them hunt a nasty nest of vampires or a witches coven for an entire season with quite a few one-off stories mixed in. Think of Justified and that series story arcs. Something more human in scale.
Make Cass human. Figure out a way to use Crowley where he isn't the all-powerful king of hell. Let's have the gang fight werewolves and stuff and forget about the fate of the world hanging in the balance.