I liked it a lot. It was of course heartbreaking but show has been hinting at Sam going dark this season and it was time to bring it or ditch it. I think Sam strangling Dean pretty much sealed it. I betting that Sam is supposed to be a vessel for Lucifer and Dean will have to kill him, or Sam will have to go all berserker with demon blood and dispatch Lilith and go full on evil and Dean will have to put him down. I'm sure it will end with a tragic cliffhanger just like Season 3 with Dean in Hell. SInce we know SPN is back for a fifth season and with my favorite new character Castiel as a regular cast member I assume Angels will be part of the season 5 arc. I know the finale next week will be an orgy of angst I just want Ruby to die horribly by Deans' hand, and don't kill Bobby. I really liked how Sams' hallucinations showed how he sees things. Mary sounding a lot like Ruby telling him what he needed to hear, and Dean telling him that God picked Dean not Sam. I really think Sam must resent that. I know Kripke and Jared talked about how while Sam was of course grateful that Dean was out of Hell, things had changed for Sam and it would be hard for him to back to being the little brother. I think when Sam agreed to let Ruby train him and began his revenge path to Lilith, he was a lot like John after the YED, nothing was stopping him, even family that he clearly does love.
I also loved how you can tell Castiel is in a very precarious position with his superiors. He can't speak freely but his eyes convey a sadness and resignation. I really dread the fallout when Dean finds out Cas is the one who set Sam free. I don't think Cas had a choice, follow orders or ??? When Anna briefly dropped in on Cas he only had time to tell her she shouldn't have come before two angels swooped in and that was that. Somehow I doubt they killed Anna, I don't know why she would still be running around and not in angel jail, but I bet we see her briefly in the season finale.