That`s right.. the fun is in the speed of the game.
But about what gta 4 needs. there are other things like.. to have your own men (gange) that obay you (Tommy) and do whatever you want from them! and also it will be more fun if there are long roads between cities ,it would be more fun to be driven for a long distances (like 2 minutes on the road!!).
one other thing... I think it should have more porn sences