Considering how massively popular the last two GTA games were Rockstar could’ve knocked out any old rubbish as their last GTA game this generation, but despite Grand Theft Auto: San Andreas not being a full sequel (it still uses essentially the same graphics engine as GTA III) it has more new features and ideas than the majority of official follow-ups.
For a start San Andreas itself is not a city but a whole fictional county, containing the San Francisco-esque San Fierro, the Las Vegas style Las Venturra and the Los Angeles inspired Los Santos. You can drive anywhere else you like in the countryside, between making the game four to six times the size of Vice City.
You can also now start up your own gang in the game, recruiting members and claiming territory--you can even build and operate your own casino once you get the necessary moolah. You can’t just sit around and wait for the money to roll in, though--eat too much junk food and your character will grow fat and have to work out at a gym, as well as keep an eye on a new stamina meter.
The list of other additions and refinements are almost endless; above and beyond the usual claims of an improved aiming system for weapons you can now swim, ride bicycles, get your hair cut, take part in random break-ins and robberies... pretty much anything you were ever told not to do as a kid (except the getting a haircut bit).