This is a direct upgrade from GTA III. Almost all the missions are really cool and take full advantage of the engine. For some reason they made the final mission of the story one of the most boring but all the rest of them make up for it. It was a tiny bit buggy at times, and any reliance on AI calls for disaster, but is significantly better than it's predecessor.

I would probably recommend people looking to get into the series to start here, this game holds up well.