1st: I freely admit I love the character of Castiel. But I also really, really had hoped that with the end of season 5 that the character would never, never appear on Supernatural again.
2nd: As many posters might remember I have been extremely upset that Dean really gets to see the bad that Sam has done, but as far as we know Dean doesn't know that Castiel is the one who set Sam free to lose Lucifer on the world (Yeah still a bit pissed about that).
SO here we are at the first appearance of Castiel, and how shall I put it. I was really, really not getting my hopes up. First I haven't been terrible impressed with the episodes (C+ and for me the 2nd a B (which generally an average episode of SN for me) and 2nd its about a character that I thought had served its purpose.
Well, I liked this episode, I liked it a lot. Its not A material, but its B+ material in my book.
First Castiel appears because it suited him. He is more like early 4th season Castiel in some ways then the humanized Castiel that was through much of the 5th season (after all why should Dean and Sam be the only ones who get to change).
We see that Castiel is a cold blooded son of a bitch. Which Dean, you really should understand. He might have been a comrade in arms (and that does form strong bonds), but he shouldn't really be your friend. His reasons for doing things are not yours and often aren't even close. We rarely get to really see that, and I always love seeing that.
Nice use of still showing Dean's connection to Lisa and Ben and also showing how much Sam is different (more of that towards the end).
Nice to see Rapheal again (I really enjoyed the menace the actor brought to the role, in his previous appearance). Nice to see Heaven's a mess.
Souls. Souls as currency, and Crowley is certain to be upping his standing in the world. assume we will have Bobby's deal come up soon. But we don't know if given the soul back was part of the original deal or Crowley just chatting about his intentions. I expect that will be covered.
Atmosphere. OK, here is what I found to be the weakest aspect of the episode. And what in my mind prevents an A- score. The show's teaser and early horror elements lacked any sort of tension or atmosphere. And this isn't the first time this has occurred. I haven't made attention to the directors or the editor, but its also possible ( I would need to see how specific the script is some are quite general on this element some are very detailed in notes ). I also need to check the DP credits to see if this is an issue.
Sam, ok I have been posting that I thought Sam might just be turning into the person we saw in his trickster induced 6 months (cold, unemotional, meticulous hunter and lacking any real feelings of empathy). I think his time in hell, his sense of responsibility for the actions he set in motion and isolating himself form Dean for a year could explain it. I still think its possible But I don't think the writers are going there. Clearly the preview is implying that Dean soon (probably in the next three or four episodes) learns some truth aspect of Sam and it freaks him out. So I think my hypothesis is clearly not the way the writers are moving the story. The question then becomes what has happened to Sam. The writers have said yes this is Sam. And I hope they weren't deliberately lying. I really don't want any bit of Lucifer tied to Sam. And clearly I don't want to see that Sam doesn't have a soul (which seems opposite of what we know about souls in SN universe). Clearly he can feel humor, and has base needs. But we have yet to see Sam experience strong emotions. From hate to love, ect.
Color me intrigued but worried as well.
That wasn't fun. 
Cas using air quotes. 
Man, those boils and grasshoppers eating brains made me want to retch. Classic SPN. 
Mileage varies, of course. C'est la vie. Ben Edlund wrote this one. I KNEW IT. 
