It sort is sort of like GTA but perhaps more colourful. In a fictionalized version of the San Francisco Bay Area, the game is played from a third person perspective and its open world can be explored on foot or by vehicle. Players control Marcus Holloway, a hacker who works with hacker group DedSec to shut down the city's advanced surveillance system called ctOS.
This game was actually only to be given away freely for an hour's time yesterday, but due to break down of Ubisoft's servers, you can still get lucky here:
https://register.ubisoft.com/ubisoft-forward-reward/