Unlike the other people who give definitions for this game, who give wrong information or none at all, this is what its about. You play Carl Johnson(CJ), who returns to the state of San Andreas after 5 years in Liberty City. To make a long story short, CJ and his brother are betrayed by Smoke and Ryder, and CJ rescues his brother from jail and gets revenge on everyone...While doing TONS of other things and meeting TONS of other people.
The State of San Andreas has 3 cities;Los Santos,(Los Angeles)San Fierro,(San Francisco)and Las Venturas(Las Vegas).
In this game you are able to do tons more stuff than before; like lift weights, buy clothes, get tatoos, get hair cuts, gamble, and do tons of other stuff that would take all day to list. But they also made it gay by forcing you to eat or else youll starve.
AND FINALLY!!!!, You can swim instead of drowning upon contact with water!
Grand Theft Auto: San Andreas is great, but its fun to go back and play GTAIII and GTA Vice City as well.