If you watched SPN 504.
Enjoy or can tolerate slash
Enjoy or can tolerate Dean/Castiel (it's there but trust me it's worth dealing with even if it's not your OTP)
Then go read :
Not all the way through It's by far the best Fic Reaction to an Episode I've read.
WHY?
For me it filled in those 5 years in a way that made me cry and hurt and want it to never, ever happen. It doesn't just complement the episode it adds depth to it.