Dean is a self-righteous, hypocritical, selfish douchebag. They get the chance to finally close the gates to hell and he backs out at the last minute. Just because Sam would have to die to do it? How did they not see this coming, after ALL they've been through? There was/is always a price for such universe-shaking spells/trials/etc. So many people died and sacrificed (esp Kevin) just so Sam can do the trials (willingly mind you) and Dean just stops it! And it looked like the trials aren't killing Sam anymore. Yet another life-save for Sam, similar to how Castiel just magically got rid of Sam's soul-madness from his time in Lucifer's cage. Something that Death himself couldn't cure and Castiel just , poof, absorbs it and later cures himself. rofl
And Sam's confessed sin of failing Dean, not living up to his expectations, and letting him down? That's not a sin! LOL
I was bored out of my skull this whole season, waiting for a payoff that didn't happen. And the whole Castiel drama was getting tired. I'm glad he's human, now he can die.
The only bright point of all this was Metatron. His revenge scheme was brilliant and chilling in its "non-evil"ness. The angels had it coming, they lost their way and only realized this too late. Best moment of the entire season (imo) was Metatron's final speech to Castiel.
"And now, something wonderful is going to happen. For me and for you. I want you to live this new life to the fullest. Find a wife, make babies, and when you die and your soul comes to heaven, find me. Tell me your story."
It's too bad Metatron was introduced so late into the series. He is a great anti-villain.
P.S. The whole procedure for curing demons was so ... mundane that it cheapens the whole idea of redemption. *Oh look, I can do all the evil I want in life, go to hell, become a demon, and just get cured after my last binge-killing! Heaven, here I come. PFFT