Simply free roaming to sight see and cause havoc is a very linear way of having fun
This statement makes me want to facepalm myself into the darkest f*cking corners of oblivion.
For me, free roaming is 50% of what makes GTA, well... GTA. Wandering around with complete freedom. Making use of the world around you to entertain yourself because you have that choice. The world is the real star and it gives you so many options for fun that weren't ever planned in detail by the developers. Making the game your own experience.
For example, and hey, I don't expect anyone to think 'hey Fuzz, you've totally changed my mind and I'm going to try this right now!', I can grab a bmx and ride all the way around the map and have fun. I can create havoc with vehicles and weapons. I can set up my own courses for dirt bikes, cars, off-roaders, planes... there's just so much to do! I can literally play the game every night for a few hours and not do the same thing once over a week. There's so much freedom, completely non-linear freedom, that is just there as a side effect of the size of the map, the variety of vehicles and the very well balanced physics system - it nods to reality while trying to retain the fun of a balls-to-the-wall Hollywood action blockbuster.
I have no problem with people preferring to stick to what the devs explicitly give them as activities as their sole forms of interaction in the world, but I do feel a bit sad that there are people that just don't even consider completely free play as something worth doing. But again, that's cool, and it's not for me to say one play style is any better than the other.