to get a game like GTA 3 to work in multiplayer you would need a lot of bandwidth.... quite a bit actually. The randomness would have to be cut out which means that every car and person would have to be tracked accross the whole map. This would mean that the maps would be smaller and their would be less interactive things (cars, people)
It is very possible on LAN with few players.
Still how cool would this game be with 2 players runnin and gunnin?
you could just specify the location of an NPC with a x,y co-ordinate and another number for their design seed, with their directions etc. being controlled by the host as normal... the maps wouldn't need to be as huge as they are, perhaps with some smaller maps for multiplayer etc.
I really hope they have better car AI this time. I found that everytime you pic up speed and you can see a car infront of you sometimes they randomly oull out infront of you, and when your on a time limit its pain in the ass.
It would also be nice if they fixed the memory leak problem. Other than that GTA3 was excellent.