A massive shift in scope with the introduction of Angels and Castiel. The focus moves from local haunts to preventing the biblical Apocalypse.
The road ends at Season 5. Everything after that is just a bonus. Supernatural Seasons 1-5
The season is a road trip through the Apocalypse: plague, famine, war, and the breakdown of society. , now rebelling against Heaven, loses his grace and regains it. The trickster Gabriel (revealed as an archangel) dies buying the brothers time. Death himself (Julian Richings) makes a deal to help. And Chuck (Rob Benedict), the prophet writing the Winchester Gospels, is subtly implied to be God. A massive shift in scope with the introduction