Because he was an angel, Castiel initially expressed almost no emotion towards humans, and had little room for disobedience or feelings, as he was driven to follow his orders, although he does reveal some doubts about the morality of his orders, expressing an appreciation for the beauty of humans as Gods creations. As he spends more time with Dean, he develops empathy and affection for him, and eventually for those close to him, and humans in general. Castiels superiors begin to question his loyalty and promote Uriel to oversee him. Castiel eventually rebels against and is ostracised from heaven, leaving him deprived of most of his angelic abilities, forcing him to interact more with humans than he had previously. He is often confused by the finer details of human interaction and is blind to social norms. He allies himself with Dean, and despite his despondency over the absence of his maker and their desperate situation, Castiel continues to fight against the Apocalypse.
After his second resurrection by God, with enhanced abilities, he sees his decisions and support of freewill to have been affirmed. Castiel begins to show pride, while remaining somewhat naive with regard to consequences. Crowley is able manipulate this budding sense of pride to get Castiel to start the angelic civil war. Castiel becomes dedicated to his own decisions, and tends to pass over other opinions, even Deans, in the absence of another clear course. He eventually double-crosses Crowley, taking in the souls of Purgatory alone. He then insists on worship from his former friends. He intends to be an involved god, a better and loving god who will not abandon the world. He renounces his dedication to free will, saying that angels need a firm hand. He is quick to smite those he feels to be hypocritical and unjust, and rewards those who have faith. However, Castiel is being influenced by entities inside him - including leviathans - and his actions become erratic and violent. He realizes he is not strong enough to contain the power, and at a prompt from Sam, he goes to the brothers for help. He is apologetic and humbled; after the souls are out of him he wants to find a way to redeem himself before the brothers. He eventually takes Sams madness on himself, freeing Sam.
In episode 5.14 My Bloody Valentine, Castiel shows his deep affection towards raw meat, eating it in the room and unable to get to famine, one of the four horsemen. Here, we realize that Castiels vessel, Jimmy Novak is desiring the food which he cannot gain access to with the angel possessing him.
Castiels insanity after taking on Sams memories of Hell seems to free him of some of his guilt, though it leaves his mind scattered. He was unwilling to fight due to his belief that he is a "jinx," though Dean convinces him to help kill Dick Roman. He also expresses some fondness for Meg despite the previous animosity that existed between them. However, after getting trapped in Purgatory, Castiel seemed to have regained his sanity, though he admitted there is no way to know for sure. However, his experiences have changed his personality somewhat and he is no longer as aloof as he usually is and has displayed a fondness for human things he took for granted such as watching television, which he never understood before.
4.01 Lazarus Rising.