Now I loved GTA III as much as the next guy(or girl) but Vice City puts that game to shame (I like that rhyme). There are improvments in almost every field of the game. Like weapons for example, there are a whole new arsenal of destructive weapons going beyond your basic shotgun. There are a ton of new cars including a wonderful addition of the helicopter. Now the seaplane is kind of odd, but it's a major improvment on the Dodo. Some other new vehicles include: motorcycle, dirtbike, rc helicopters and rc cars, new boats and other new basic cars. All in all, GTA VC is a new level of theft
The graphics didn't change much from GTA III to VC so there wasn't much improvment in the area. Don't get me wrong the graphics in VC are still spectacular but they were the same in GTA III as well.
There are so many more missions dispite the sad fact that there are only two islands. You go from doing the drug baron's bidding to living in his mansion. With the free roaming mode to top this game off Grand Theft Auto: Vice City is one of the best games ever made.