In theory, the Imperial system isn't necessarily evil. It is essentially feudalism, where the strong gain power, and the weak swear allegiance to them. A great deal depends on the character of the leader. A good, strong leader can make life a lot better for her followers.
In practice, though, the Empire is evil. Power corrupts, and the strong stop caring for the weak, and treat them with cruelty and injustice. As well, the Emperor is out and out evil, and he sets the tone for the entire empire.