Light was a gigantic piece of shit and a simple serial killer. There's no question, even if L was doing this out of some devotion to a game and not out of empathy, it didn't really matter. You're talking about a morality vs. deliberate action, killing anyone who stood in his way for whatever reason, even if they were just. He tested it at first, then clearly enjoyed the killing with the God-Like power associated with it. The guy even killed his own father without giving a fuck. There is absolute no doubt he was a total sociopath from the beginning.
The problem is Death Note sort of craters once L is killed through sheer bullshit which is the main problem with Death Note. The cat and mouse game between Light and L was basically the entire series. What happened doesn't feel organic and the writers realize what a problem they are in. So they fiat it in. Then the last part they sort of just stumble through.
Matsuda is so awesome because Light gives this grandiose speech about some bullshit and monoluging, and thinking he's an unkillable Godlike villian, when he just got fucked ten ways from Sunday and Matsuda just fucking fills him with holes. The Ryuk just writes Light's name in and he ceases to exist, his soul consigned to oblivion. He dies so pathetically, its great
