Samyaza's legacy is one that etched itself into the world forever. He stood at the head of the most powerful, wise and righteous band of creatures to ever walk the face of the earth. That sort of power would corrupt any of us. If only he hadn't succumb to it, there would be no bounds to what the Watchers could have achieved.
Despite the fact that Samyaza's actions brought humanity to the brink of destruction and doomed hundreds of angels to damnation. Despite this, I don't want to fully denounce his actions. His sin is pride, an emotion we all have a mixed experience with. It's a complicated feeling that comes with as much temptation as it does danger.