A lot of caveats to this list:
1. I started watching Supernatural in 2005, so I originally watched it week-to-week, way back when Netflix still came in little onion-skin envelopes in the mail. The 35mm film first 3 seasons have a forever hold on my heart. The search for Dad, Azazel's children, the writer's strike, Dean's speech in "All Hell Breaks Loose Part 2," it's carved into my ribs in Enochian.
2. I am a Gen-Xer like Dean, so I get all of the references and already knew all of the "classic" rock. I still laugh when I think of a fic I read that included the line "Dean's favorite songs were ancient before he was born" and I was like "Dude, 'Back in Black' was released when Dean was 1, and 'Traveling Riverside Blues' didn't get an album release until 1990 when Dean was 11. When do you think Dean was born??"
3. I adore Sam and Dean, think Cas was only great in Seasons 4 & 5, and that bringing people back as ghosts is dumb.