-You can flip off other characters in the game, and see interesting results dependent on who you're flipping off.
-Vehicle physics have been updated. "The cars hold to the ground a bit better". It now feels more like a racing game, compared to GTA IV where they felt "big and boatlike".
-After a hiatus in GTAIV, Ammu-Nation is back!
-A lot of new side activities, including yoga, jet sking, base-jumping, tennis and golfing on a full golf course!
-Rockstar felt that dating wouldn't fit in this game and have stripped this feature.
-Bowling, Strip Clubs, Live comedy, Internet cafes and in-game TV make a return.
-Mobile phone will return, but friends won't be calling as often as they did in GTAIV. It will be more streamlined and used for things like emails and Internet browsing.
-Random character encounters throughout the map, much akin to those in GTAIV - but this time there's a greater variety and they're fully motion captured.
-Dynamic missions, similar to Red Dead's "Random World Events" make a return. Examples include characters with broken down cars, a hitch hiker, or two parked cars with dead bodies around them - which you can investigate to initiate dynamic missions.
-Dynamic "state machines" were coded in the game, allowing non-playable characters to go about their daily lifes. For example, you may see gardeners and cleaners waiting at the bus stop in the morning, and then find them tending the gardens and houses in the game's fictional Beverly Hills later on in the day.