So, this episode response is considerably more coherent then most of my others. I only watched it last night. It was amazing!
Semi-grovelling Sam at the end of the episode really irked me. Other than that, I mostly liked the episode. I think my heart broke for Castiel a little bit. At the same time, I wanted to smack him. Really. Being human isn't THAT bad. When Dean was talking to Sam a light bulb clicked on in my head. Part of Dean's reason for separating them was to prevent the powers that be from using their relationship against them. It made a whole lot of sense to me.
I don't know if any of you are C.S. Lewis fans, but I think Dean would be. (Lewis's entire reason for writing Screwtape Letters was to counteract the image of Satan that Milton presented.) Dean's disbelief about Lucifer's "sympathy for the devil" act is right up Lewis's alley. I almost cheered for him. When Lucifer called us the hairless chimps, I wanted to go, "Hah! You're just jealous because YOU aren't made in the image of God. If you really loved Him, you would love us too." It made me happy when Dean essentially told him to shove it.
Also, for those of you who hated Dean for the things he said about Sam at the end of 5.03, I learned something interesting in my psychology class. I believe that Dean was essentially suffering from cognitive dissonance. Cognitive dissonance occurs when a person has two conflicting ideas at the same time. These two ideas cause tension. The person will then change one of the ideas in order to alleviate that tension. Sam is Dean's baby brother, who he loves, who he has protected, who he GAVE HIS SOUL to save. He is also caused (with help) the Apocalypse. Sam also chose a demon (who Dean repeatedly said he didn't trust) over Dean. These two ideas (the brother he loves and the bringer of the apocalypse) are in conflict with one another. To relieve that tension, Dean has to change one of the ideas. He can't change the second one. The evidence for it is staring him in the face. So, he tries to change the first one. It's not that he really believes what he's said. He's just trying to ease the confict going on inside himself. It's human nature. (Please know that I do not think that Sam is solely responsible for the apocalypse. There are a whole lot of people to blame.)