Cannot wait for this
I agree with Kklein, it would've been nice to see somewhere new but still looking forward to it though. Falsey's probably right the returning character is probably Lazlow...but i find it's strange the way they worded it - Lazlow was in all the last gen GTA games, not just San Andreas.
They went for the "rags to slightly nicer rags" story with Niko...i'm hoping for a return to rising to the top of a criminal empire in GTA 5. It's amazing just how many features GTA 4 was lacking but hoping they bring back things like being able to buy properties, lets us buy shops again, more shops in general, etc.
One feature i liked in GTA 4 and i hope they develop it further is the whole choice thing in some missions. I'm hoping that we get more choices like that in missions but this time round they have a greater impact on the story. Another thing i think they could do is provide perhaps story arches. Say if you fail a mission....it shouldn't be a simple case of redoing it, perhaps the story could develop along a different path if you...let a drug dealer get away or fail to stop a character from getting killed. Things like that will add even more replay value to the game.
Car customisation should make a return as well.
One feature that was hyped up but didn't quite deliver was the whole cell phone thing. If they bring it back they should give us more freedom, let us make the calls to characters to inform them that we've done or failed a mission. Maybe even let us ring up friends to help us out on some missions or even be able to socialise with multiple friends/characters at once.
Another thing i think would be cool in a game like GTA is if they copied Fallout 3's "random" events feature. In Fallout 3 you'd stumble across things like Brotherhood members fighting a deathclaw or random people just coming up to you needing help, in GTA when you're in free roam we could see scripted events like a gang attempting to rob a store or rival gangs meeting up to have a gang fight or gangs having a shootout with cops - just things like this to make the city a big more believable and more alive so to speak. Speaking of cops, here's hoping their AI is beefed up and they're made to be a bit more believable as well. Hopefully civilians/AI will be capable of committing more crimes so the cops pursue them more as well.
Stereotypical or not, Tommy Vercetti is by far my favourite GTA main character. I didn't mind Niko to be honest. I didn't like the Mafia characters in GTA 4 to be honest, not a patch on the characters like Salvatore Leone from the "GTA 3 universe".
Those are only stuff i can think of off the top of my head, i can probably think of a ton more stuff i'd love to see in the next GTA