Now don't get me wrong. I think that the antagonists in every book are interesting and intriguing. For instance, Valentine was once like any other Shadowhunter: fresh, obedient, educated. But he was too ambitious for the Clave, and instead of seeing its good, he saw all of the little faults. I think that if he hadn't turned evil then he would be AMAZING. As with Sebastian. When he's not planning in raping Clary, he's not a bad guy.