Closest thing to GTA at the moment is Manhunt, which is Rockstars latest game using a modified GTA engine.
In terms of violence, its 100 times worse then all the GTA games conbined, has heaps of profanity (first game I ever heard to use the F and C words, not to mention the term \'fagg0t\') and has much more smooth graphics compared to GTA.
Try it out if your into that sorta thing, but be warned its pretty hardcore.