Saying GTA3 did well because it was violent misses the point. The violence brought the game publicity.However: if you ask people about why they liked the game, they will say it was becasue it was fun. This is the conclusion I've come to after asking a good number of people (all avid gamers/game developers), reading a lot of articles about it, and of course playing it.
It is faulty logic to say that because a game is fun and has violence, that all violent games will be fun. Or even to say that violence always makes games fun.
The fact of the matter is that violence was just one factor of the whole game design of GTA3 that made it fun. Without all the aspects that made the actual gameplay as great as it was, it would have flopped despite the ability to run over people etc. The fact is, many games have had that ability and others like it, and didnt go on to sell 7 million copies.
Unfortunately, people today arent very good at basic scientific/logical principles. The key one here being: corollation does not equal cause. GTA is very violent. GTA is very successful. It does not necessarily follow that it is the violence that makes it successful. The violence just gets it free press. The game still has to live up to that by being fun.
Let me contrast GTA with another game that is similar in many respects, yet has no violence. The Sims. Personally, I'm not into the Sims that much, but it has plenty in common. It has sold bajillion copies, it's still selling well. It has mass market apeal. It is set in a contemporary world with attention to detail. It provides loose goals to gameplay but encourages exploration and improvised gameplay. In short, for a very wide cross section of people the game is very fun. The game has mass appeal.
So does GTA3. Part of that appeal for many people is the violence to innocent bystanders. But unlike games like postal 2, where that is the focus, GTA also appeals to a lot of other people who get off on other things like the cars, the music, driving around, the hookers, doing side quest missions (like police, etc.). It's appealing to a lot of people, not just the RWS types. And unfortunately for Postal 2, I think it lacks the appeal of games like GTA3. Yes, Postal 2 will get lots of press. But press wont be enough to make the game appeal to normal people. That is of course merely my own prediction of the future based on RWS description of gameplay, but I'd like to think I know a thing or two about good game design.