I've heard City of Heroes/Villains is pretty good; I know it has a subscription fee. It's a superhero/villain game where you create a hero (or villain) and team up with other created heroes (or villains) and take on your opposites, basically, of whom are also created by others.
If you really wanna play a GTA inspired MMO, you're gonna have to wait, unfortunately. There' going to be APB for the PC (Consoles are being considered). APB includes an extensive character creator and you can either be a criminal or cop.
Other MMOs to watch for:
DC Comics Universe (PS3/PC) - 2009
Much like City of Heroes/Villains, where you create your own DC Character and fight in various DC cities, such as Gotham and Metropolis, against DC villains and created villains.
Huxley (PC/360) - 2009
An FPS MMO which features 80 vs. 80, or more, campaigns, PVP, and character creation. It's powered by Unreal Engine and plays more like Quake and Unreal than Halo and Call of Duty.
The Agency (PC/PS3) - 2009
The Agency is a more Bond-ish MMO. You're in one of 2 agencies and you're assigned to missions with other players.
Champions Online (PC/360) - 2009/10
Another superhero game, made by the creators of City of Heroes/Villains. It's cel shaded and resembles actual comics, where you craft a hero or villain from a robust character creation system and choose your power and such.
Star Wars: Knights of the Old Republic MMO (PC/Unspecified Consoles) - 2009/10
If you've ever played KOTOR for the Xbox, you know what this is. This will probably involve you creating a Jedi or Sith Lord and team up with other Jedis or Siths in a struggle for the Republic's survival.
