According to ESRB, this game contains: Blood, Intense Violence, Strong Sexual Content, Use of Drugs and Alcohol, Partial Nudity, Strong Language

Parents should keep their children far, far away from this game. I know that all of their friends are going to be playing it, but seriously, you're a parent. Grow some backbone. The content listing should have made the point clearly enough, but just in case you don't know what those words mean, let me make this absolutely clear: among other things, the game features strip clubs, endless headshots, drug dealing, implied and threatened torture, and plenty of offscreen sex. If your older teens beg for it, fine, but it's not to be played by anyone who confuses fantasy with reality.
GTA Fans can rejoice, this is everything that you had hoped it would be. Sure, all of the RPG elements of San Andreas have been pruned out, but the tradeoff is a fantastic story and incredibly entertaining multiplayer mode, so don't be too sad that you can't make Niko eat burgers until he's a waddling tub.
Deaf and Hard of Hearing gamers should be pretty safe with this one. The onscreen HUD is great at keeping you oriented, the subtitling extends even to some of the incidental dialogue, and Niko's in-game cellphone can even be set to vibrate, so the controller shakes in your hand whenever you're getting a call. Rockstar North has really shown a dedication to accessibility with this one.