If you actually had stuff to do online there would be no problems. For them to achieve what they have done however (A huge environment you can roam with 7 of your friends) is worthy of much praise, but there needs to be goals, achievements and such for it to be worth playing.
GTA 4 multiplayer suffered for many reasons; There was few civilians to maul, you couldn't partake in missions, races and the like, but imagine a living city full of civilians you could kill, banks you could rob, police you could have full-blown shoot-outs with etc etc.
Don't forget though, a game is only as good as its community. You look at some of the videos on youtube where people have took the time to organise games and create their own game-modes to realise the potential of these games.
I did hear RS were contemplating adding stuff to the free-roam though, such as poker and tougher gang hideouts, but they could just be rumours.
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I'm still avoiding this thread though as I've only just arrived in Mexico and people don't seem to be using spoler tags.