Two of my favorite things about SPN are the fact that Dean's best friend in the whole world isn't even human, and the idea that Castiel is basically using Jimmy's body as a puppet. And I like drawing a trueform!Cas interacting with Dean. This image may be a bit creepy but I'm not even a little sorry.
In a lot of ways, the thing with Castiel is almost more science fiction than anything else. He's a pure energy being with apparently quantum characteristics (the guy's a wavelength!). He's an alien consciousness. 'Heaven' and 'Hell' in the context of the show are less mystical states of transcendence and more semi-physical locations with their own native inhabitants. There's so much potential there with that alien-ness. And though I love the ways Cas has changed in response to Dean's influence in his life, I'd love to see something exploring the ways Dean could change in the other direction.