In a large open world like GTA5's Los Santos, third-person perspective gives you a nice complete view of your surroundings. If you've ever wanted to get inside Franklin's head, though, a video from modder XBLToothPik shows what Grand Theft Auto would look like as a first-person shooter.
The answer is: a little funny, and also a little disturbing. Los Santos is well-rendered enough that even the closer perspective doesn't look bad, and so it makes for a nice a casual stroll down the sidewalk. Then Franklin starts shooting, and something about the first-person perspective makes that a little creepier. After all, most of the time when we shoot things in first-person, they're robot zombie Nazi aliens, not civilians. No wonder Rockstar is sticking with this third-person thing.