Will go down as one of the most influential games ever
But if you take all 3 games and where they compare the day they were released, GTAIII is the revolution, and the other 2 are just evolution. Never before had a video game offered such an immersive, 3D sandbox environment and let you do whatever you wanted in it. The shear number of clones of this gameplay style is the proof : the sincerest form of flattery is imitation.
If you didn't know, GTAIII puts you in the shoes of a convict that catches a lucky break on his way to jail, and now has to work his way up in the underworld of a living, breathing city modeled on modern day New York. Along the way, you run missions for various bosses, play cabbie, cop, fireman, and ambulance driver, drive a wide variety of cars and trucks, shoot pedestrians in the head from atop parking garages, and pretty much anything else you can think of! It's not unusual to spend hours in between missions exploring, or just causing havoc and then trying to avoid the police. The fun factor is insanely high.
It's the city itself that makes the game. Liberty City feels just like a modern day urban environment. It has distinct neighborhoods (Red-light district, Chinatown, Skyscrapers in downtown, even college neighborhoods) with distinct inhabitants and "feel". The gameplay on the PC is excellent, with a FPS-style WASD+Mouse setup, and driving with the keyboard works fine. Flying the plane is a pain, but fortunately is a very small part of the game.
This is the game that broke open the mold of "sandbox" titles, where you are given an immersive environment and set free to do whatever you want. Vice City and San Andreas expand this formula, but this game created it. It will go down as one of the most influential games of this decade, and maybe ever.