The problem with that analysis is that Vice City was specifically designed as a single player game. Throwing in a multiplayer component there wasn't the best idea ever. But if there was an MMO GTA, designed around the concept of gang wars, it could be a blast. Rockstar knows what they are doing.

Have you played two player mode in San Andreas? It proves that Multiplayer in GTA can work. But that mode is severly limited by having a single screen. Online is the only way GTA multiplayer could truly be worthwhile.