The story about the doctor was creepy though especially with those plague masks, though the premise did remind me a lot of Asylum from season 1 with that Doctor Ellicot guy. And I just felt so sad for those kids, especially Sean when Dean talked to him in the veil and he told Dean he couldn't leave that place and wanted to see his mom. :( Also, the scene earlier when the boys wanted to question him and Dean was talking to him while he drew those pics...reminded me of the little boy Lucas from Dead in the Water (again from season 1).
It was pretty cool to see Billie again, though making her Death even after Cas killed her...that's something I wouldn't have expected. It was interesting how she told Dean that he and Sam have work to do, and that she wanted info about the alternate world. Looking to collect some bodies from there, I assume? Perhaps anyone we might know?
The ending... Liked the boys talking there, Dean admitting he's not okay and that they need a win. I'm also happy to have the classic rock back (Steppenwolf I believe that was?), but the way they filmed that reminded me of the other CW shows, with the classic rock over those emotional scenes. And then the phone call, and..... bum bum bum!! Cas is back! Why am I sorta underwhelmed?
Again I liked the old school feel to it...still trying to sort though the whole Billie died and is therefore Death now thing. I guess there was a power vacuum with Death having been killed by Dean, so...who else was there? I dunno, still scratching my head over this one.