It was a great episode and i like the idea that Dean is Gods choosen warrior like Sam was lucifers. For the last two seasons its bin bout sam having deamon blood in him and how hes to be the great leader for hell at the side of yellow eyes. Deans just the by stander trying to protect his brother. The fact that Dean is infact Gods choosen is a work of genius on the behalf of the writers.
I think its understandable that Dean was choosen as well. For what we've seen Dean has sacraficed everything for his family and obviously for others he sacrifices a chance at a normal life to protect others. He also willingly went to hell to protect Sam showing he will go to unusual lengths to protect sam. Naturally Dean is also the only one who can save sam from himself. If Sams loosing a part of himself every time he uses his abilities its natural that only dean has the potential for stoping sam as i think sam could never kill his own brother. That bond is too tight and would betray the very essance of the show.
i also love the person acting out Castiel. The writers were fantastic showing the doubts and vunerable side to the angel and the relationship forming between him and dean is touching. The line where castiel was praying that Dean would choose to save the village was also touching as it showed that he understands and sees the goodness in Dean.
But besides the obvious excellt script work i wanted to mention the fantastic special effects and the general location teams. The effects have improved so much since season 1 and i'm loving the new way they've come up with for sams special exersising deamon abilities. Its the subtel things like the mark that burns on the floor under the victims that helps to make this a visually exciting season as well.
The whole supernatural team is just amazing :D
Love this episode and Dean ;) season 4 is brillient :P