The problem I see with Aizen is that he's so ridiculously powerful, God-like and distant that it was only recently in the manga that we started to know what his true motivations were. At least with Light Yagami from Death Note we could see how he thought and how he strived to create the perfect world from the very beginning.
He's charismatic and bishounen, which makes him attractive and palatable. Plus, the scene where he goes 'Superman' on the entire Soul Society after obtaining the Hogyoku is priceless.
He spent all those years playing the 'nerd' captain, the tender, calm and spiritual one, just to find out that it was an illusion from his zanpakuto, Kyoka no Suigetsu, able to achieve total and complete hypnosis.
Not to forget how he stopped Ichigo's bankai with a finger, and the whole groupie relationship with Hinamori is just sadistic.
But overall, he has a sorta pimp personality (only rivaled with Grimmjow) that is reminiscent of those nostalgia villains from the 80's, just with a more suave touch.