Let's just look at some of the comparisions
-Both were regular 17 year old high school students, who felt that their lives were meaningless, and that they repeated the same boring lifestyles day in and day out, both wanted to do more, change the world around them, but lacked the power and motivation to do so.
-Both were good looking and very popular with the ladies
- Both met immortal supernatual beings that granted them great power, power that they used to become vigiantees and shape the world in their ideal image
-both came up with alternate identites to converse with the public, "Kira" and "Zero"
- Both have a legion of followers who would like to see them succeed in their goals, for Light it's Misa, Teru Mikami, and the Kira Supporters, for Lelouch, it's the Black Knights and the suppressed Japanese public
-Both have genius level intellect and are master tactians
-Both have a flair for the Theatrics
-Both break the law to enact their own brand of "Justice"
-Both were extremely arrogant at times