Depends what you mean by mature. For me, despite all the high ratings and concerns over gore, etc. games likes Gears, Army of Two, Modern Warfare, etc. are all far from mature. In fact, I'd argue most are actually fairly childish.

Mature for me means adult context and themes explored in an adult way. And really, certain themes aside, that doesn't even mean it has to require violence or language.

Heavy Rain looks like it might get it right, but I'll reserve judgment until I play it. After all, QD's last title started very well and looked like it was going to handle mature themes well, then went to hell in a hand basket from about the half way point in.

Well since people said God of War ill have to say Gears of War. Especially 2. Gears of War 2 went way to over the top especially with the language. it kinda added to its childish effect of trying to be too Bad ass

In this content, mature is more along the lines of the rating.  I know what you are talking about tho.

How can a person have that much blood? Gta and Dead Rising

GTA4!!! alot of the fun stuff from San Andreas is missing and you can get a wanted level far too easily, the franchise tried to grow up when its userbase did not want it to

also I do not care about my stupid fat cousin!

Killzone 2, without a doubt.

Killzone 2, Gears of War 1+2, Wet(Though I guess the over the top feel of it was the whole point of the game....), Army of Two & 40th Day, Modern Warfare 2 (For the commercials alone).

Dragon Age : Origins tries too hard too be mature, but in the end you feel like was made towards pubescent teenagers. All related to sex in that game is very teenish, we don't reaaly see real mature content. But that game is marvelous.

MW2

GTA4 in terms of gameplay and narrative

Gears of War does at times try too hard to be "hardcore". I'm surprised no one on the first page mentioned House of the Dead: Overkill; the profanity in that game was absolutely senseless. Seeing as to how it was only 2 hours and they fit all the cursing in there was ridiculous.

God of War is warranted I think; it captures that mythological Greek brutality, but some parts are a bit much (slamming the guy's head into a book/slamming it with a door repeatedly).

Dead to Rights 2 was one of those overachievers.....there was one standout game but I forget what it was. Maybe X-Men Origins Wolverine, or Wanted: Weapons of Fate, I don't remember....