I like Sam as a character. It's been fun to speculate about what is up with him and to see fan reaction to what it might be. I'm guessing he's either possessed and trapped in his own body or that a big chuck of him is missing or frozen. It was really creepy to watch his reaction as Dean got turned. Kind of a skeevy, sick fascination. Jared's doing a pretty good job given that he's sort of playing a new character that is rooted in the work he's done with Sam for the last 5 years. He's not really taking on a different character like Lucifer or Meg so much as having to reinterpret the character he already knows so well.
I'm liking this season a lot so far but I hope we start to get some info about what's up with Sam. Always in the past, even when he was demon-blood-drinking Sam, he's always been a sympathetic character. It's really weird to feel like he's a bad guy now without really knowing why.