I loved the way they introduced Jessie's character and how they developed the entire episode. Of course they having the kid on their side could have been really cool... but way too easy, so having the boy leave for now was the way to go. I also loved the twist on what the Antichrist really is, not only original but very cohesive with the plot.
In the other hand I can't stop wondering, has Sam lost all of his power? I mean, he had psychic "abilities" before all of the demon blood stuff.
Also, I think Castiel's character is becoming more human with time. He now knows when to lie and how to speak to other humans so his cover isn't blown (I'm not sure it's intentional though.) I still remember him acting all uptight and awkward around others.
Thinking far into the future and considering both Jessie being good and bad, I'm not sure which I prefer. Sure I'd like him to be all-good but having him as an enemy would translate into a much greater challenge for the Winchester boys (right?) and that could be pretty interesting.
I guess we'll have to wait and see!