This was a story that made me go 'wow'. The crumbling relationship between Sam and Dean, Cas becoming less angelic and more of a dick, and wearing Dean's expressions, yes, that was perfect. Sam's odd fear of replacement, while at the same time needing to be away from Dean. you managed to pin down a very complicated triangle of relationships.

I loved Cas's magic, and Sam seeing parts of Castiel's true form and just being blown away by it. Castiel's slide towards his Croat-Future self was also very well done, moments and comments and actions, and it became that little it easier to see how he ended up where he did in that future.