They can be overly and unnecessarily violent, but I feel that when a game uses violence to make a point or for the sake of comedy...or just to give a game identity, it's perfectly fine.
Take Assassin's Creed for example. This is a series where you play as assassins. Your goal is to kill people, often times. But one noticeable difference between Assassin's Creed 1 and all the rest is that 1 was a lot more tame than the others, and appropriately so. You could see that, despite whatever feelings Altair had for the victims, he respected them as humans at the very least. The others, on the other hand, often go out of their way to make these grisly deaths for their victims...and often not for much reason other than...maybe to attract a crowd? I would say that AC has been moving its way towards the unnecessary scale since 1, and while that doesn't necessarily make them worse, it does get you to think.
What's more, kids and teens do play these games, and while I won't say that it makes them more violent, it does get them to play with the idea of death. I don't think it'd be a case of The Raven, but people do get interested in these murder weapons and ways of killing. Do I think this is the games' fault? No.
See, movies (and shows) are FAR more available to the average person than games are. Games have to be bought, or at the very least downloaded. Movies are everywhere, and they can be far more violent than games can. What's to stop a child from accidentally seeing a slasher flick that just happened to be on? Heck, Scream was all about the subject. I wouldn't blame games for something that movies do on a larger scale.