I've been watching the first season of Buffy the Vampire slayer between stuff from Netflix and it is interesting going back having seen all seven seasons of Buffy and five seasons of Angel. You just know more stuff.
Interesting tidbit of the day: In the Season 1 Episode "Nightmares" one of Buffy's nightmares (fears) is that the Master will break loose and he will bury her alive. Flash forward to the first episode of the sixth season after Buffy sacrificed herself to stop Glory, Buffy is dead and she is buried. But when Willow's spell brings her back to life, Buffy is buried alive. There's some continuity! And it was only natural due to the story arc, but watching the early episodes knowing how everything turns out is interesting.