Evil? I don't see anything evil in what he did. He is a man of ideals, Aizen believes that if he can't rule the world then no one can. He didn't allow himself to become subjected by the Soul King, he wanted to change the world.
Well he only wanted to usurp soul king's throne or whatever but he did kill some pple in his attempt to creat the hougyoku so yeah he is.
nice question though and another one wld b is Madara evil.