First off, bad news everyone, take a deep breath, sit down, grab a tissue or your pillow or puppy, kitten, bunny, frog, lizard - whatever it is that helps you get through bad news. Okay. Is everyone set? Good. I'm sorry to have to be the one to tell you this but Hellatus is halfway done. That's right. I'm sorry to say that we have reached the mid-point of 2010 Hellatus and there's nowhere to go but quickly into the new season. 
Everyone all right? Okay. Remember, together we can manage the fact that soon Hellatus will be all over and there will be nothing to do but enjoy a new episode of Supernatural each and every week.  Darn. Jas' couch is always open so pile on if you need to.
Now, with the bad news out of the way it's time to give a little love to Castiel. Castiel stormed onto the scene at the beginning of Season 4 and I for one can't imagine my Supernatural without him. Like Bobby Singer, Castiel quickly stole my heart. 
Enter one bada** angel with a mission for Dean from God. One of the coolest entrances ever.
Castiel is curious about humans as evidenced by his flipping through the spell books Bobby had on the table as well as his incredulous realization that Dean doesn't think he's worth saving. That doesn't stop him from quickly getting down to business and he doesn't brook any of Dean's insolence at the end of Are You There, God, It's Me, Dean Winchester:
"You should show me some respect. I dragged you out of hell, I can throw you back in."
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It doesn't take long for Castiel to start to find some sympathy for Dean and what he's facing though. Castiel's purpose in sending Dean back in time in In The Beginning was to speed up the learning curve and get Dean on board with how long Azazel has been putting his plan into works, however, Castiel learns a little something along the way; he cares.
 Castiel's next appearance has him meeting Sam for the first time; still unaccustomed to human interaction it's a very uncomfortable meeting for both:
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While Dean continues to generate sympathy in Castiel for all that he's facing, Castiel is still focussed on his mission and being resolutely loyal to heaven, thus his appearance with his new angel-sidekick Uriel is decidedly not filled with forgiveness nor sympathy for the choices some have made: 
"Anna has to die."
And yet, at the end of Heaven and Hell, Castiel's sympathies arise again, this time for Anna.
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There is a four-episode break in Castiel appearances and when he returns at the end of Death Takes a Holiday and captures Alastair there is something very Cheshire Cat about his appearance, Cas is clearly pleased with his cleverness.
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All is not good for dear Castiel though for as we now know, Alistair was never to be captured and once he was, Dean was to be killed by him and Castiel was to remain thinking the demons were behind the recent death of angels. We now have every reason to believe that Zachariah and Uriel were working together behind the scenes in some fashion or another, although I don't believe Zachariah wanted Dean to be killed but he didn't mind the death of angels from what I can see, so it's likely that Castiel's new restrictions and his loss of authority were directly attributable to Zachariah's orders.
Castiel's conflict grows exponentially in "On The Head of a Pin" as he truly sees the toll his angelic orders are taking on Dean and through Anna's pointed comments and his own ability to think Castiel starts to realize that he's being played a fool and free will starts to take hold, the smallest nugget of it to be sure but it's a start; and the burden is heavy.
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Monster at the End of This Book shows that while Castiel still maintains his loyalty to heaven he's learning how to play a little outside of the lines. He truly can't interfere with Dean's desire to get Sam out of town rather than a chance a face to face with Lilith, but Castiel has learned that you can still tell the complete truth and yet provide your now friend the information necessary to save the day.
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Sometimes, however, in trying to help people you forget to cover your tracks, and you forget just how clever your bosses and/or frenemies are at catching you out. The Rapture gives us a glimpse at a little lesson Castiel gets for straying outside of the line. Was his punishment meted out by Zachariah? Probably, for Zachariah needed Castiel to keep Dean in line and assist in manoeuvring him into the corner that Dean found himself in during When The Levee Breaks. So in The Rapture, Cas is snatched from his vessel and given some heavenly punishment that is more rocky road then heavenly hash. [I'm going to an ice-cream social with friends tomorrow, so you can see where my focus is]  For us it's a chance to meet Jimmy, and there have been times since then, especially in My Bloody Valentine, when Jimmy has peeked out of Castiel's eyes.
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Castiel is allowed back into Jimmy's body but it is clear that all is not as it had been. When the Levee Breaks finds Castiel with zero sympathy for Dean's distress over Sam's demon-blood addiction, instead we find Castiel cornering Dean and forcing him to vow to submit to the will of heaven, likely something that was necessary in order for Zachariah to imprison Dean in the "green room" in Lucifer Rising. [We know that Adam went willingly with Zachariah in Point of No Return as he was intent on finding his mom, so it is likely that Dean's initial willingness to submit was a requirement for imprisonment, that's my thought.]
Still, Castiel's conflict over forcing Dean to submit to the will of heaven and his subsequent betrayal of Anna are weighing heavily and he is not the same warrior angel that vowed he would throw Dean back into hell if Dean didn't give him some respect. Even when forcing Dean to submit, we can see the conflict.
At the end of Season 4 Castiel has made his decision, he's choosing between what his orders are and what he now thinks to be right and they are mutually exclusive; there will be hell to pay come Season 5.
So there you have it, part 1 of a two-part look at Castiel's changing role. Stay tuned for Part 2, coming up.
Thanks for reading, Elle2