According to Game Informer Issue 190, Rockstar may be on track to deliver a new GTA title by the end of this year;

"We're not talking about new DLC or a collection of previously available DLC, we're talking about a full retail game. We expect this title to follow the suit of previous GTAs and use a subtitle such as GTA: San Andreas, etc. Tokyo might be a possible setting for the game, but details are non-existent at this time."

This would seem to follow on with the rate of expansion show with Grand Theft Auto III, as Vice City only trailed by a year or so. If this is true, one question will remain - now that Rockstar have a solid foundation, can they improve the depth of the story and silence GTA IV critics?