I think Sylar's power to understand things and absorb them, like powers, has fed his ambition and he's not evil but he has an uncontrollable urge to understand how everything works and to become more powerful and more complete and he believe the best way to do that is other people's powers
Good and Evil are terms used by people to rally more people. But it is a term that everyone can use and does use to contradict the other side
For example WWII the Germans believed they were "Good" while their enemies were "Evil"
While the rest of the world believed the Germans were "Evil" and they themselves were "Good"
The rest of the heroes may think in terms of good and evil
But somehow I dont think Sylar does