Better Gaming: Infinity Blade And Real Racing 2 HD
Most games aren't taxing enough on mobile graphics processors that you'd notice a difference between the iPhone 4 and 4S. If you're accustomed to playing Angry Birds and filling out crossword puzzles, there's really no reason to buy an iPhone 4S for its added graphics muscle. The PowerVR SGX 543MP2 is simply overkill.
On the other hand, if you enjoy games like Infinity Blade or Real Racing 2, you will see clear improvement. The developers behind those titles include code paths able to exploit Apple's latest hardware.