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troperville

Sam and Dean are shot to death by a pair of angry hunters and find themselves in Heaven. They are contacted by Castiel, who asks them to find Joshua in the hopes that he knows where God is. Sam and Dean must make it to the Garden in the middle of Heaven without letting Zachariah find them and return them to their earthly bodies. They travel through a series of their fondest memories. Dean becomes angry at Sam because several of Sam's happiest moments were times when he got away from his family.

After a reunion with Ash and Pamela, Sam and Dean are cornered by Zachariah. They're saved by Joshua, who tells them that God has a message: back off. God knows everything that's going on, but he doesn't think it's his problem. Joshua returns Sam and Dean to Earth. They pass the news on to Cas, who is devastated. He gives the amulet back to Dean, who throws it away as they leave the motel.

Tropes

Almighty Janitor: Joshua has a lot of authority for a simple gardener.
A Form You Are Comfortable With: Even in Heaven, Dean and Sam perceive Zachariah in his vessel, the same way he appears on Earth. In an interesting variation, the terrain follows this as well: the Axis Mundi (the road through Heaven) appears as a two-lane blacktop, and the Garden of Eden as the botanical gardens in Cleveland where Dean and Sam once took a field trip as children.
Badass Boast:
Zachariah: "I'm the last person in the whole of creation you want to mess with".
Continuity Nod
Death Is Cheap: It's Lampshaded: "When I come back, I'm gonnna be pissed." "You guys die more than anyone I've ever met."
Despair Event Horizon: Poor Castiel.
Fluffy Cloud Heaven: Averted. Everyone literally gets their own slice of Heaven which will be whatever they expect/most want it to be, and filled with replays of their most treasured memories. It's very personalized, but also very singular. Once in your little bit of Heaven, you're stuck. You can't go and visit others, and only soulmates get to share.
God and Satan Are Both Jerks: God knows what's going on, he just doesn't care that Satan is going to destroy the world. This may actually be a subversion, as a later episode implies that Chuck is God and has been helping (as a prophet) without hand-holding (as God) the whole time.
Heaven: Heaven is made up of zillions of Happy Places, with the garden of Eden at the center. You're generally alone in your personal heaven, unless you have a soulmate (or you're Ash). Dean is dissatisfied with this rather lonely arrangement, describing it as "The Matrix".
Roaring Rampage of Revenge: The hunters shoot Dean to prevent Dean from doing this after they kill Sam.
Suspiciously Apropos Music: Knocking on Heaven's Door — in Heaven.
What Happened to the Mouse?: Roy and Walt, never seen nor heard from again, despite Dean's promise.
- Theory: Considering how Zachariah was looking for them in Heaven so that he could bring them back to life, maybe he dealt with Roy and Walt before hand...