SPOILERS READ AT OWN RISK!
It was emotionally jarring (I was sobbing by the end and almost couldn't enjoy Percabeth's kiss!), and the twist was so unexpected. I loved how Luke was so human. Usually villains are very cardboard. They are told to us as evil, and that's how they act: evil. But Luke was different. Even before his ultimate sacrifice, he was constantly going back and forth between evil and good. He wasn't purely evil or purely good, and I loved how that complexity gave depth to his character.
The scene itself was so good! Because he had constantly been conflicted about the whole affair, until he made the choice to be the hero, I honestly thought he was going to be the first person in the history of the world to go against the prophecy of the fates (and that NEVER happens). But in the end, he did the right thing (and tore my heart right out, but ya know, saving the world is more important than my bleeding heart D:) . What really got me was that it was ultimately Annabeth's promise that brought him back. The love he had for her (brotherly- I think) was enough for him to pick a sure side and stick with it- even if it meant his own death. You can't get more heroic than that.
*goes off into a corner to sob D:*