1. All three protagonists are completely customizable. They can be altered to a point to where they don't even resemble their original selves. Don't like Trevor's balding hairstyle? Give him a mohawk and a big goatee. Does Michael's clean look bother you? Shave his head and give him a massive beard. The variety in clothing is huge. Trevor, Franklin, and Michael will change their own outfits if you leave them unattended long enough.
2. The car damage is MUCH improved since Rockstar's last GTA installment. Each type of vehicle reacts different to damage. A truck will be able to take more physical damage than a standard car would. Heavier vehicles will destroy lighter vehicles upon contact. The stronger the vehicle, the more it will take for damage to be dealt to its exterior. Vehicles CAN be upgraded in a body shop with armor. It's pricey, but it will make your vehicle withstand more damage.
3. If you are a Rockstar Social Club Member, you will get bonus content upon playing the game. This includes new hairstyles and beards, a new gun, and a few other nice goodies. If you reached the maximum level in Max Payne 3's multiplayer, you will also get bonus content.
4. Forklifts, Bulldozers, and Tow Trucks are fully operational. You control the scoop/lift/hook with the left joystick.
5. Chop has a full list of commands. He can be told to wait, attack, or even fetch. His ball is located in your grenade slot.
6. Random Encounters was introduced in Red Dead Redemption, and it's making it's way to GTA V. Spontaneous events will randomly happen throughout the world, and it's up to you to do something. You walk into a store and see two muggers robbing the place. They run out the door with the loot. Do you chase them down and get the money back, or let them go? Do you kill them and take the loot for yourself, or return it for a reward? It's up to you to decide. There is dozens of Random Encounters throughout San Andreas.