Actually, if it wasn't for the ending, I would have said this was one of the best supernatural episodes yet. I just wanted to hug Sam through the whole thing, he was perfection. And lucifer! Man, I hope he's in more episodes. Seriosuly, the noise that came out of my mouth when I saw 'Mark Pellegrino' in the opening credits was not human XD
But just... I wish they'd either killed Cas, or made him the leviathan straight away. I didnt like how he came back and then turned into the Leviathan. It just got my hopes up, and when they were dashed... I felt queazy. Had to go write some porn to make myself feel better XD