Wavelength Of Celestial Intent. Whoever created this, should know that this is my favourite fan art of Castiel.
I don't think Cas become anything he wasn't meant to be. The thing about Castiel is he's not quite like other angels. He's more...human. He can wonder about right and wrong and how he affects the world, not just heaven or hell. The other angels lost their purpose, but not Cas. He still remembers the purpose God gave them. Even though things don't work out the way they are supposed to, he's trying and knows when he's messed up but he still keeps trying to make it right.
tarot by ~natira on deviantART (Dean Winchester, Sam Winchester, Supernatural Fanart)