I've been playing video games for my whole life, since DOS oldies. And I can safely say it's changed me, I'd be ignorant to say otherwise. Positively and negatively, I'd guess.
I wouldn't know how to speak english, for one. Negatives - I'm cursed with being a gaming addict, being antisocial and such. Hell, if given enough free time, I'll use it to play games. 10 hours? Eh, done worse. But there's a bright side to this addictions - I have no other addictions, such as smoking or alcohol addictions.
But the rating system doesn't address the most crucial part of games - addiction changes you, not the violence in them. Once the game is diverse enough, it becomes addictive, and once the game has a competitive component, it truly prolongs the time the game can be played as well as chances to be addicted.
So anyways, I see the rating system more as a safeguard for the game developers and publishers themselves, so it's easier to deal with disgruntled parents who think it's the games who corrupt their kids. They need something to blame, they don't want to just say, eh, he just happened to be a psycho, they don't want to admit it. Take for an example the Halo Killer, Daniel. We do not know anything about his attitude, personality, social life that he had prior to when anything serious happened, or so I presume from what I've read. Maybe the parents were oblivious to what happened in his life, or were hoping that, if his attitude was weird, it's just temporary, or just a phase he's going through.