I never read a character so puzzling for me. Even though I haven't read lots of manga, so yeah
He was the only villain I ever
cheered for. He wanted something good. Started like this angel~ with a goal. He did. Yet, in the process, he became truly evil, for me. But I still wanted to see him suceed, and I'm not a villain-liking type. I can't say the reason though. The charisma was just too strong. His relationship with others while being the secret Kira was also really good.
And his intellect, omg. That's more about the whole Death Note though. But his plans were epic.