One of the first things I ever nerded out about was Star Trek. It was something to watch with my dad and I loved it. TNG will always have a special place in my heart even though I haven't watched it in fifteen to twenty years.
One of the most shocking, I-have-to-see-what-happens-next moments that I ever first experienced was the season finale of the third season - when Picard steps onto the screen of the Enterprise no longer a man but Locutus of Borg. I don't think I knew of the concept of a season or a finale until that moment, but I could never forget after that.