A leaked post on Rockstars site might have some more info on that. Has since been pulled from the net. But luckily enough the internet, got ahold of some of the improvements.
Increased draw distances, finer texture details, denser traffic, and enhanced resolutions all work together to bring new life to the cities, towns, deserts and oceans of Rockstar North’s epic reimagining of Southern California.
All new content and gameplay created since the launch of Grand Theft Auto Online, including an extensive array of new Jobs, an arsenal of new weapons, scores of new vehicles, new properties and player customizations will also be available for the PlayStation 4 system, Xbox One and PC with much more to come. In addition, the current community of players will have the ability to transfer their Grand Theft Auto Online characters and progression to their choice of PlayStation 4, Xbox One or PC.
Grand Theft Auto V for PC will also feature a video editor designed for advanced movie-making.
A brand new first person mode for vehicles that shows the interior of the vehicle, including working speedometers, tachometers, dash lights, and more
A brand new first person mode while on foot
A wealth of new easter eggs and random events for Story Mode
New animals roaming Los Santos
Animals in GTA Online?
Players that transfer characters from Xbox 360 or PS3 will receive free new weapons and a free garage in GTA Online.
Newly overhauled character selection screen
We will have to wait until the 18th November for the Xbox One and PS4 versions to find out. PC version out January next year.