Oh, so much to think about!
I've only read about five episode reactions, as I capitulated to sleep about ten minutes after the episode finished, so I don't know if this is just the same stuff everyone else is posting (my usual reason for not posting my thinky thoughts). So.
First of all, I was *so* impressed by both Jared and Jensen last night. Jared's face in the scene where he's questioning and then killing Alistair? That was a beautiful, complex, balanced look on his face - it was less "yay! killing!" and more the pride of an artist, a pleasure in his own competence. I was really impressed by that.
And I liked that Sam's instinct in this episode was to stand up for and stand by Dean, to try to do what Dean tried in "Heart" - to say, no, my brother shouldn't have to do this because it will hurt him too much, destroy him, and I'm willing to stand in his place. I adored that.
The question of how Sam got his power? I really didn't like Ruby's smile, but it got me wondering if what Sam needs is not Ruby's blood, specifically, but any blood voluntarily offered (though of course only someone who's in on the game - Dean, a demon, or an angel could realistically offer blood), and Ruby knows that and is determined to be the one there for Sam. I don't know if I'm being clear here. I would love for Sam's power to be less about demon blood and more about choice and sacrifice.
My regard for Castiel was sky-high after "Lazarus Rising," but after that, he hasn't impressed me or been, frankly, all that interesting to me. But last night - how stupid was he? Alistair says - while trying to kill Castiel - "I wish I knew how to kill one of you" and it's clearly true that he has no idea. And yet, when Sam shows up and starts questioning Alistair, asking not only "who is killing the angels?" but also "how are the angels being killed?" Castiel doesn't say anything about Alistair not knowing the answer to the second question, and just gapes dumbly at Sam. Meaning that Sam has to keep expending his energy on controlling Alistair, and Dean and Castiel himself are both kept waiting for medical attention. And let's not even get into the fact that after asking Dean to torture Alistair, Castiel waited outside like a huge wimp.
About the angel whose death opened the show: I thought that was a fantastic moment, so characteristic of this show. Because not only was the angel a fragile-looking blonde woman in a long white gown - the kind of angel many other shows would have offered without irony, where we get muscular, conniving, complex figures - but also because the camera, spinning above her, captured her, bright against the darkness, bleeding and jumbled, and reminded us of the other beautiful blonde woman who started the show: Mary, as she was splayed and bloody on the ceiling. That was amazingly done.
And Uriel's treachery - I really loved that reveal. Because it's both shocking and not. We thought, as an angel, that he would be a good guy, but we also have seen that he has never had any patience with our boys, that he has always looked down on humans - even those fighting by his side. So his character stays consistent. And of course, Lucifer was an angel too. And Uriel's choice gives, in hindsight, a wonderfully shivery feel to that flickering moment when he smiles at Dean and claims to like him, because of course he likes that the person he picked as his sacrifice will go out fighting.
(Aside: Anna and Uriel both using the nickname "Cas" really bugged me. But what if they were both doing it to get under Castiel's defenses, since he clearly is invested in Dean?)
As for Dean. My poor beloved boy. I don't think I can even talk about him. I just want him to win and rest and be happy.