I would say GTA Vice City it was radical with cool atmosphere and the scenario was just AMAZING! I really like that game, with that release rockstar games shown the world what a free-roam game should be! Don't forget that before that game there was GTA3. The transition between 3 and Vice City was like traveling million light years away! From basic free-roam we went to a huge atmospheric game. Although I didn't like the fact that Vice City was too "flat" but the night pov of the city was gorgeous! It was the first GTA that presented motorbikes and Assets! Basically VC created the basis for the next games of the series! San Andreas was amazing too but now I can see that it was something like an experimental game, because Rockstar presented many many new things that not everybody loved. But that's just my opinion, I'm a big fan of all the games of the series and love them for different reasons, I'm just a liiiiittle bit bigger fan of GTA VC!