Cass going rogue, power-hungry was a neat heel-turn, and sacrificing himself as an act of redemption was touching. Bringing him back in e17 or so, quickly and weirdly revealing him, reincorporating, and then sidelining him was weird. Sam and Dean being willing to leave him in the care of a demon was WTF territory.
Sam's Satan-is-my-copilot PTSD seemed like it had been proven to be all in his head, but "transferring" it to Cass, and being something which could take an angel out of commission - implausible. If it turns out that Satan was just fucking with Sam and pretending to be only in his head as a game, and then Trojan-horsed his way into Cass? That'd be brilliant. Also, almost certainly a retcon.
The "big bad" of this season, the Leviathans, are generally pretty lame. They're inconsistent in their tone other than callous dismissiveness and a fatal willingness to regularly underestimate Sam and Dean. More than that, the groping way the show tried to tie them to HP Lovecraft is misguided and shows a fundamental misunderstanding of the author's oeuvre. Leviathans are just demons with different weaknesses. A missed opportunity to do a fresh take on that material. They should have just attributed it to a different author, or pastiche of period horror.
Still enjoying the interaction between the characters.
Bobby. Man, that was a rough way to go out. A great episode with more good interaction between Rufus and Bobby, but I seriously haz a sad over Bobby.
