Among the greatest games of all time.
Take the role of a small-time hood bound to make a name for himself. The local gangsters will send you on missions, and it's up to you to steal cars, rob passersby, beat people senseless (once you pick up a bat or pipe, you have to do it, it's just something that happens!), firebomb garages and whatnot. Lurk in gang-infested neighborhoods, hunt down mobsters, and generally break every rule but the law of gravity.
Gorgeous design too, with infinitely detailed cities, filled with wiseacre jokes on everything from classic pop music to old-school action movies. From L.A. to Miami and all points in between, you are in for one of the most absorbing video game experiences of your life.
There are really no words to adequately describe how much fun GTA is. Play it. Worship it. It's beyond my powers to stop.