The game is reportedly 3 times bigger than Vice City and bigger than the total area of all five previous games.

Here are some new things to do:

• consuming of food for stamina
• exercising
• bicycles
• swimming
• 4-person drive-bys
• home break-ins
• independent night animations
• real-time reflections

Those are basic, the ones below go more in dept about the new features!

• Entire state of San Andreas included, meaning three cities will be present in the game, each connected by countryside. Los Santos, a fictional Los Angeles, San Fierro, a rendition of San Francisco, and La Venturra, which is the Grand Theft Auto version of Las Vegas.
• Larger map, which is much more interesting and "alive" than Vice City. Hills have been confirmed, and even a mountain is to be included, which is tall enough to take up to ½ a minute to ascend in a helicopter.
• Tweaked Vice City engine, which can support up to four times the draw distance in rural areas compared to the previous game. Real time reflections, on metal areas of cars, and real time mirrors will be included.
• Improved transition between night and day, with a more immersive feeling included in each.
• Control method improvements mean strafing is now possible.
• A great deal of effort has ensured that countryside areas look and feel organic, with rivers, forests, rolling fields and desert areas. The development team has also improved urban areas by rounding off what would previously be 'square', right-angled corners.
• Smog will be present in Los Santos to give it a "real life" feeling.
• "Characters from the past" will return, with links to previous titles included for the 'hardcore' fan.
• In La Venturra, set up a casino, or gamble in those owned by others.
• Recruit gang members and perform four person drive by's.
• Pedal Bicycles.Tapping the X button will move the bicycle forward.
• House robberies will take place but require skill and planning.
• Stamina Meter. Carl will have to consume food on his journey across San Andreas, and will gain weight if he eats too much. Gyms will be available to work out in.
• Hairstyling will play a prominent role, and will allow every user to create a unique experience for themselves. Pedestrians may poke fun at characters with outlandish looks.
• Countryside areas feature unique vehicles which won't appear in the urban areas, such as a quad bike.
• Police officers gain a new mode of transport, the motorcycle.
• Swimming is now possible, however, the game is not about swimming, and drowning is still possible. If players take a car into the water, the stamina meter will again come into play, and will offer a limited time to escape the vehicle, through a window or otherwise.
• Bouncing cars will be included, with the right analog stick controlling it.
• Improved control methods allow for new fist-fighting maneuvers, and the gun physics have been totally overhauled to provide a far more immersive experience.
• During a chase, police may try to jump and grab on to the trunk of your car.
• Artificial Intelligence has been vastly improved, with police reacting more like those in real life, and each pedestrian acting though they have a 'brain'. This also allows for stealth techniques to be employed by the player.
• Each city will feature many unique vehicles which won't be found elsewhere. For example, police helicopters will have their own lettering depending on their city of origin.

These are just a few new things San Andreas has to offer!

"We are extremely humbled by the success of the Grand Theft Auto series and it has made us push ourselves further than ever to create a title in Grand Theft Auto: San Andreas that will hopefully redefine the Grand Theft Auto series and revolutionize open-ended gameplay and video game production values."