The core gameplay consists of elements of a third-person shooter and a driving game, affording the player a large, open environment in which to move around. On foot, the player's character is capable of walking, running, swimming and jumping, as well as utilizing weapons and basic hand to hand combat. Players can steal and drive a variety of vehicles, including automobiles, boats, airplanes, helicopters and motorcycles.

The open, non-linear environment allows players to explore and choose how they wish to play the game. Although storyline missions are necessary to progress through the game and unlock certain areas and content, they are not required, as players can complete them at their own leisure. When not taking on a storyline mission, players can free-roam and create havoc (e.g. drive-by shootings, robberies, etc). However, doing so can attract unwanted and potentially fatal attention from the authorities. The more chaos caused, the stronger the response: police will handle minor infractions, whereas undercover cops, SWAT teams, the FBI, and the military respond to higher wanted levels. (Wikipedia)

Cheats:

Armor:
Press Up, Down, Left, Right, Square(2), L, R during gameplay.

Weapons (tier 1):
Press Left, Right, X, Up, Down, Square, Left, Right during gameplay.

Weapons (tier 2):
Press Left, Right, Square, Up, Down, Triangle, Left, Right during gameplay.

Weapons (tier 3):
Press Left, Right, Triangle, Up, Down, Circle, Left, Right during gameplay.

Destroy all cars:
Press L, R(2), Left, Right, Square, Down, R during gameplay.

Faster game time:
Press R, L(2), Down, Up, X, Down, L during gameplay.

Slower game play:
Press Left(2), Circle(2), Down, Up, Triangle, X during gameplay.

Faster game play:
Press Left(2), R(2), Up, Triangle, Down, X during gameplay.

$250,000:
Press Up, Down, Left, Right, X(2), L, R during gameplay.

Full health:
Press Up, Down, Left, Right, Circle(2), L, R during gameplay.

Lower wanted level:
Press Up, Right, Triangle(2), Down, Left, X(2) during gameplay.

Raise wanted level:
Press Up, Right, Square(2), Down, Left, Circle(2) during gameplay.

Wanted level never rises:
Press Up, Right, Triangle(2), Down, Left, X(2).

Overcast weather:
Press Left, Down, L, R, Right, Up, Left, Square during gameplay.

Rainy weather:
Press Left, Down, L, R, Right, Up, Left, Triangle during gameplay.

Foggy weather:
Press Left, Down, Triangle, X, Right, Up, Left, L during gameplay.

Sunny weather:
Press Left, Down, R, L, Right, Up, Left, Circle during gameplay.

Clear weather:
Press Left, Down, R, L, Right, Up, Left, X during gameplay.

Pedestrians attack:
Press Down, Triangle, Up, X, L, R, L, R during gameplay.

Pedestrians have weapons:
Press Up, L, Down, R, Left, Circle, Right, Triangle during gameplay.

Pedestrians riot:
Press R, L(2), Down, Left, Circle, Down, L during gameplay.

Pedestrian enters your vehicle:
Press Down, Up, Right, L(2), Square, Up, L during gameplay while in a vehicle.

Spawn Rhino tank:
Press Up, L, Down, R, Left, L, Right, R during gameplay.

Spawn Trashmaster:
Press Down, Up, Right, Triangle, L, Triangle, L, Triangle during gameplay.

Destroy all cars:
Press L, R(2), Left, Right, Square, Down, R1 during gameplay.

Perfect handling::
Press Down, Left, Up, L, R, Triangle, Circle, X during gameplay. Note: Press Down to make your car jump.

Black traffic:
Press L, R, L, R, Left, Circle, Up, X during gameplay.

Chrome traffic:
Press Right, Up, Left, Down, Triangle(2), L, R during gameplay.

Traffic avoids you:
Press Up(2), Right, Left, Triangle, Circle(2), Square during gameplay.

Pedestrians follow you:
Press Right, L, Down, L, Circle, Up, L, Square during gameplay.

Upside down:
Press Square(3), L(2), R, Left, Right during gameplay.

Upside down (alternate):
Press Left(3), R(2), L, Right, Left during gameplay.

25% of multi-player bonuses unlocked:
Press Up(3), Square(2), Triangle, R, L during gameplay.

50% of multi-player bonuses unlocked:
Press Up(3), Circle(2), X, L, R during gameplay.

75% of multi-player bonuses unlocked:
Press Up(3), X(2), Square, R, L during gameplay.

100% of multi-player bonuses unlocked:
Press Up(3), Triangle(2), Circle, L, R during gameplay.

Commit suicide:
Press Right(2), Circle(2), L, R, Down, X during gameplay.

Unlockables

Completion bonuses:
Successfully complete the game 100% to unlock unlimited ammunition and the intermission sequences.

Car delivery bonus:
Deliver all 32 vehicles to The Civil Asset Forfeiture impound yard to unlock free Pay N Spray usage.

Shooting range bonus:
Successfully complete the shooting range challenges outside Phil's place at the Vice City Docks to get discount prices at Ammi-Nation stores.

Balloon bonus:
Pop the indicated number of hidden balloons to unlock the corresponding weapon at your safe house.
Pistol: 10 balloons
Scorpion submachine gun: 20 balloons
Stubby shotgun: 30 balloons
Molotov Cocktails: 40 balloons
AK-47: 50 balloons
Armor: 60 balloons
Flamethrower: 70 balloons
Equalizer scoped pistol: 80 balloons
Sniper Rifle: 90 balloons
M249 machine gun: 99 balloons

Business bonus:
Take over all 30 businesses to get bulletproof business vehicles.

Fire fighter bonus:
Successfully complete 15 levels in the fire fighter missions to become fireproof.

Paramedic bonus:
Successfully complete 15 levels in the paramedic missions to have unlimited sprint.

Vigilante bonus:
Successfully complete 15 levels of the vigilante missions to get extra armor.

Maximum health increase:
Successfully complete 15 levels in the air ambulance missions to increase your maximum health.

Unlimited energy when swimming:
Successfully complete 15 levels in the beach patrol missions to never tire while swimming.

Jumping taxi:
Complete over 50 fares in the taxi missions to be able to press Down to jump while driving a taxi.

Alternate costumes:
Complete the indicated task to unlock the corresponding costume in your safe house.
Army Fatigues: Complete the "Last Stand" mission.
Casual: Complete the "Conduct Unbecoming" mission.
Cuban style: Complete the Umberto mission "Strand".
Hired muscle: Buy a "High Roller" protection racket building.
Hood: Buy a "High Roller" robbery building.
Leisure: Buy a "High Roller" prostitution building.
Mr. Repo: Buy a "High Roller" loan shark building.
Pastel suit: Buy a "High Roller" drug dealing building
Smart suit: Complete all missions for all six empire types.
Smuggler: Buy a "High Roller" smuggling building
Track suit: Buy a "High Roller" drug dealing building.
Trailer trash: Complete the "D.I.V.O.R.C.E" mission.
Wetsuit: Win all eight Jetski races on the Jetski at the film studios.
Winner's Outfit: Complete the "Last Stand" mission.

Some gameplay footage can be found below (not to be viewed by persons under 18 years of age... like that's gonna stop you):