3. Season 6: Buffy's Resurrection
This moment in the opening episode of season 6 is the defining moment of this entire season of Buffy and rightfully so. Although a lot of people criticized season 6 of Buffy for being too dark and depressing, Buffy never gave the fans everything they wanted and this is a good thing because frankly, fans don't know what they want. Had Buffy had just been brought back to life and had been super happy about it the fans would have been just as annoyed. Most TV series' would have done just this, but what makes Buffy truly one of the greatest of all time, if not THE greatest, is that it didn't. Buffy was pulled out of heaven (or something resembling heaven... as an atheist, Whedon kept the show very vague as to whether or not God actually existed) by her friends, and spent a good half of this season completely depressed because of it, although pretending to her friends that she was happy. This whole dynamic changed everything for Buffy... it made her partly resent her friends for making her go though hell on earth when she could be experiencing an eternity of bliss and it was arguably the biggest catalyst in her future relationship with Spike. Also, this was the most difficult spell Willow had ever pulled off, and was partly responsible for Willow's ego boost and power trip she would take later on in the season which would make her lose control, go to the dark side, and attempt to destroy the world. Buffy's resurrection is also the explanation given for why, in the final season of Buffy, the First is able to take out the slayer line.