To me, a game doesn't need ultra-realistic graphics or heavy processing for it to be excellent. I feel it's all about the art style they use in games. Games like Uncharted try to make a "realistic" impact so more horse power (in the PS4) would be needed for the next level of realistic detail.
But I think for most well-designed games with a certain art style that doesn't necessarily stress processing capabilities the PS3 is good enough. Most games (other than games like Uncharted and God of War) do not use the full potential of the machine. I personally don't like games with a realistic look to them, I prefer more artsy games like Tekken.