Hunters murder Sam and Dean making it possible for the brothers to not only knock on heaven's door, but to go "behind the wall" where their mission impossible becomes finding Joshua, an angel that talks to God.
I'm going to preface this by saying "Dark Side of the Moon" is a stellar episode of Supernatural. Having said that, it's also one of the most difficult episodes of Supernatural I've ever watched and blogged. On a scale of 1 to 10 the show cranked up the angst to about a hundred and fifty. "DSotM" is one of the most devastating episodes of the demon-hunting series ever and that's saying a lot. This is a good thing because the Winchesters are in the midst of an apocalypse and an apocalypse ain't pretty. It's dark, it's depressing and there are multiple opportunities to lose faith. I really wish this one had followed "My Bloody Valentine" because Dean's descent into despair would have flowed even better in my opinion.