It will be just like Witcher 3 or GTA V. Just roam about freely, do whatever you want.

Rob ATM Machines, shoot people in the face you don't like, walk into shops and buy clothes and food or new guns.

There will be jobs and side quests on the map, some points of interest (not as many as W3, though.) You can put off doing any quests and just walk around the city doing nothing. There's no levels or "free roam", the whole game is free roam.

You're free to go anywhere you want, or do anything you want. Have sex with almost anyone you want. (You can bring people back to your apartment for a one night stand.)