4. Season 5: Buffy's Gift
This is probably the single most iconic moment from the entire series, and probably the episode most people think of when you mention Buffy The Vampire Slayer. This episode, the final episode of season 5, "The Gift" would completely changed the show from then on. In this episode, Buffy sacrifices herself in order to save her sister and dies, but not before the most epic battle in the entire show (edging out Angel and Buffy from Season 2) and perhaps in TV history. This battle is so full of edge of your seat action and multiple plot twists that there really is nothing more exciting you could possibly watch. Like mentioned earlier, Buffy the show likes to keep Buffy's battle plans secret until the best moment to reveal them, and this battle was no exception. Most of Buffy's confrontation with Glory is actually not Buffy at all, but the Buffy-bot. When Glory defeats the Buffy bot and we realize that she had been fighting a decoy all this time, Buffy swings what is effectively Thor's Hammer (maybe Whedon looked into his future and was getting the practice in) into Glory's face to announce her presence, and the battle against time is really on. Buffy eventually however is too late to stop the impending apocalypse like she had been when she was forced to kill Angel, but instead of making the decision she had done in her youth- to kill Angel to save the world, this time she realized she had a choice, and could make amends for her actions in the past. Instead of sacrificing her sister to save the world, she instead sacrificed herself, and more than this, was completely content and happy to do so. However, Buffy's death didn't last all that long...