Season 2 expanded the lore significantly. We learned the truth about the Yellow-Eyed Demon (Azazel) and Sam’s psychic abilities. This season solidified the tragedy of the Winchester lineage, introducing the concept that Mary Winchester’s death was part of a generational curse.
It was about Dean getting the pie, Sam getting the family, and the two of them finally resting. Supernatural Season 1-15
The Mark comes off. The "Darkness" is released. It is Amara , God’s older sister and the embodiment of creation itself. This season is the return to form. For the first time in the show's history, the Winchesters meet God (Chuck Shurley, the prophet). The resolution is beautiful: God reconciles with his sister because the Winchester brothers taught him the value of family. Season 2 expanded the lore significantly