Let's get the most important part out of the way: The game is due for a May 2013 release date. This totally falls in-line with Rockstar's release schedule, where they will face little competition, and will likely take over the world.
The main protagonist is Albert DeSilva, a half-hispanic man that was once part of a Vice City crime family. He's the "rich guy" from the GTAV trailer, and he's got a son named Kevin. His son is your sterotypical CoD player: lazy, obnoxious, spouts racial slurs, and likes FPS games. Rings a bell.
Gunfights are more reaslistic. Example: If you're pulling a drive-by and shooting out a window, aiming is all over the place, as it would be IRL.
Police AI is advanced. They won't fuck with you over small things like crashing by accident. At one star, they'll chase you on foot; no sirens or shooting. Two stars, they use stun guns unless you have a weapon drawn, then they'll shoot. For three stars, you'll see Cops-style chases, where they'll kill everyone around to stop you. At four stars, shit gets real. Police will don riot shields, throw flash bangs. Radio stations will be interrupted with descriptions of you and your crimes, warning citizens. Even if you manage to evade the police, they'll keep searching for you for another 24 hours, looking for people that match your descriptions. At five stars, they shoot to kill, pulling out all the stops. Again, if you manage to evade, they hunt you for 48 hours.
Radio stations will do traffic reports that are reflected in-game.
The game will have a real, working economy where you can sell drugs, cars, weapons, and god knows what else, to fund your crime-ring.
Last, but not least, and probably the best news for me, is that there will be a playable demo at E3. I'm skepticle here, though. Rockstar hasn't been at E3 since 2007... when they demoed Grand Theft Auto IV.