Two great articles address the differences in the “Visual Experience” for Grand Theft Auto IV, the first is a video comparison of in game footage from Joystiq and the other is the resolution and effects used for each system by Kotaku. Now to really understand what is going on, you should read the Kotaku article then watch the video. You will be more prepared on what to look for.
When you’re watching the footage, it starts out with in-game movies so you can see exactly synced views. The first thing that jumped out to me was the coloring and lighting effects on the PS3 version. They look more flashy and alive then the pale and less filtered colors on the Xbox 360 version. When it switches over to in game footage you can see that the effects make the game a bit more lively looking. It’s hard to describe in words, so check it out for yourself.