Yeah, I realize GTA-esque might mean different things to different people, both good and bad.
When I say GTA-esque Im mostly talking about the sandbox nature of the adventure. The adventure mechanically conforms to the way your PCs are playing it.
For example, if you have a high "Heat Meter" rating, you will have more violent confrontations with the cops. But the best way to raise your Heat Meter up high is to be violent.
So the more violent your group is, the more violent the adventure is.
There's also three alternate endings, based on your PCs' actions during the adventure.
So the experience of a group who shoots and steals everything in sight will be fundamentally different from the group that acts subtly and tries to help the NPCs they run into.