A HUGE jump forward!
The world is living, you have so many random events.
I recommend to play the game slowly, not rushed like i do, because at the release, the game had no multiplayer, after ~2 weeks, rockstar games unlocked the multiplayer, so everyone was rushing through the singleplayer, which was a mistake.
You have hours of hours to play with all the sidemissions.
In my opinion this game is one of the best in the GTA Series.
Tiny Spoiler: You have three playable characters, everyone with his special ability, after you played a while, you will unlock them, because you cant play at start everyone.
The fourth character is your online character and yep THIS TIME you can play most of the singleplayer stuff, online.
If you play offline like in every gta game, you earn money, but this time ONLINE too!
So you can play online and put your money to your virtual bank account to buy stuff online in the virtual internet.
No matter if you want buy a car, a bike, a boat, a plane or even a freaking TANK.
But to buy that vehicles, you need an apartment.
To get money you can rob shops, kill other player, do missions and on.
You also can buy weapons in the weaponshop, like in every gta, but this time online =)
There tons of Minigames online and offline, you can play
Triathlon, Tennis, Golf, Darts, Hunting, flightschool, shooting range, street racing, parachute, yoga.
AND the official GTA 5 Editor is now released, you can make your OWN MISSIONS!
If you don't have this game, but it now, you will not regret it, if you like the gta series.