I just bought GTA4, should I buy a DualShock controller now?

May be...

I already have 2 regular controllers. I'm concerned that if I'm getting shot in the game from the back I'm not going to realize it. Is it worth an extra $55?

the dual shock is pretty sweet. i had 2 of the regular sixaxis controllers, but i traded one in....the dual shock does both functions...vibration and the regular tilt functions of the sixaxis......it's totally worth it.

YES YOU SHOULD THE MONEY YOU PUT INTO THE GAME SYSTEM I WOULD BUY AND EXTRA ORIGINAL DUAL SHOCK CONTROLLER. YES. YOU DO WANT TO MISS THE FEEL OF THE ACTION.

Yeah you should. Sony's dumbest decision, not to include a vibrate feature in their controllers. What were they thinking...